Godet introduces this section with this comment...

The new principle had just been laid down. The apostle had found it in the object of justifying faith. But could a principle so spiritual, apart from every external and positive rule, take hold of the will with power enough to rule it thoroughly? To this natural objection, formulated in Ro 6:15, St. Paul answers as follows: by the acceptance of grace a new master has been substituted for the former, sin (Ro 6:16, 17, 18, 19); and the believer feels himself obliged to serve this new master with the more fidelity because he rewards his servants by communicating life to them, whereas the former master pays his by giving them death (Ro 6:20, 21, 22, 23). Thus it is proved that the new principle is clothed with sufficient, though purely internal authority, to control the believer's entire life.  (Romans Commentary - Online)

WHAT THEN?: Ti oun:

The question with which Paul introduces this verse is emphatic and expects a positive answer and thus some version translate it with this emphasis:

"Surely you know that" (TEV)

A T Robertson writes the following notes on the Greek text...

What then? (ti oun) Another turn in the argument about the excess of grace.

Shall we sin? (hamartesmen). First aorist active deliberative subjunctive of hamartanō. “Shall we commit sin” - occasional acts of sin as opposed to the life of sin as raised...in Romans 6:1) (where the practice of sin as a habit -present tense - is here raised )

Because (hoti). The same reason as in (Romans 6:1) and taken up from the very words in (Romans 6:14). Surely, the objector says, we may take a night off now and then and sin a little bit “since we are under grace.” Another turn in the argument about the excess of grace.

Wuest comments that...

"This second question proposes a life of planned infrequent, spasmodic acts of sin, since grace makes it impossible for a Christian to live a life of habitual sin. Paul answers this question in Romans 6:16-23 by showing that the Christian has changed masters, and that serving the Lord Jesus, it is not his nature to sin." (Wuest, K. S. Wuest's Word Studies from the Greek New Testament: Studies in the Vocabulary of the Greek New Testament: Grand Rapids: Eerdmans)

SHALL WE SIN BECAUSE WE ARE NOT UNDER LAW BUT UNDER GRACE: hamartesomen (1PAAS) hoti ouk esmen (1PPAI) hupo nomon alla hupo charin: (Ro 6:1,2; 1Cor 9:20,21; 2Cor 7:1; Gal 2:17,18; Eph 2:8-10; Titus 2:11-14; Jude 1:4)

Shall we sin (264) (hamartano) means to miss the mark (and so not share in the prize). It means to act contrary to the will and law of God.

Under (5259) (hupo) frequently meant not simply to be beneath but to be totally under the power, authority, and control of something or someone.

Law (3551) (nomos) (click for purpose of the Law illustrated) is etymologically something parceled out, allotted, what one has in use and possession; hence, usage, custom. It refers to formalized rule or set of rules prescribing what people must do. Sin will overcome us if we try. All attempts to defeat the flesh in our own power will fail.

Grace (5485) (charis) is God's unmerited favor. It is that power which enables me to "turn off" my flesh and to overcome sin.

Ray Stedman says that Paul's sense here is...

"Should we sin even once now that we are not under law but under grace?"

Kenneth Wuest paraphrases it...

"What then? Shall we sin occasionally, because we are not under law but under grace?"

Montgomery paraphrases it...

What then? Shall we commit an act of sin because we are not under law, but under grace? Certainly not.

Here are some other ideas conjured up by Paul's question

“Shall we sin just a little?”

"If forgiveness is as easy and as inevitable as all that, if God's one desire is to forgive men and if his grace is wide enough to cover every spot and stain, why worry about occasional sins?

"Why not do as we like from time to time? It will be all the same in the end."

The answer to "shall we sin?" is "Absolutely not". And he will explain why such a false teaching cannot be accepted.

The question in this verse arises as a reaction to Paul’s statement that now...

“You are not under law, but under grace.” (Romans 6:14)

This question is similar to the one at the beginning of Romans 6:

What shall we say then? Are we to continue in sin that grace might increase? (Romans 6:1)

Note that there is a difference in the way these two questions are phrased. 

In the first, the Greek verb "continue" is present tense and thus refers to a life of habitual sin.

In the second, the verb tense (shall we sin) is aorist tense and thus indicates that here Paul is referring to occasional, single acts of sin. The thought is,

“Since your doctrine of superabundant grace teaches the impossibility of a life of habitual sin on the part of the Christian, will the fact that a Christian is not under the uncompromising rule of law but under the lenient scepter of grace, allow for at least an act of sin once in awhile?”

The idea that grace is "lenient" compared to the uncompromising rule of law, is an erroneous one. The Holy Spirit indwelling the child of God, is infinitely more cognizant of sin in the life of the saint than any system of law ever could be. He is grieved at the slightest sin.

In the first question, the desperately wicked heart offers an excuse for sinning in that a life of habitual sin gives God an opportunity to display His grace and thus glorify Himself, which is of course a perversion of the teaching of grace.

In the second question, this same person seeks a loophole somewhere in God’s plan of salvation whereby he might sin once in awhile, and thinks that he has found one in the fact that the Christian is now under grace and is beyond the reach of the law of God which could condemn him. Therefore, he argues that he can sin with impunity, and grace will always forgive. Can you see Paul's argument?

One can see at once from what Paul tells us in Ro 6:1-14, that the person who asks such a question as well as the one in Ro 6:1, is an unregenerate sinner. The child of God has no desire to go on in habitual sin nor yet to sin once in awhile. To be sure, a genuine believer is at times guilty of willful sin. That is, he may yield to temptation, knowing that it is sin. But to provide for a planned life of infrequent acts of sin, is altogether foreign to the nature of the saint. Paul answers this question as he did the first one, by the words “God forbid,” “far be the thought.” Then he uses an illustration to show that it is a mechanical impossibility for a Christian to desire to sin even once in awhile.

John MacArthur sums up Paul's argument...

With his brief introductory question, What then? the apostle again anticipates the false conclusions his antagonists would derive from his declaration that believers “are not under law, but under grace” (verse 14b). To them, the idea of no longer being under law but under grace was tantamount to being free of all moral restraint. “If the law no longer needs to be obeyed, and if God’s grace covers all sins,” they would argue, “then believers are perfectly free to do as they please.” Jewish legalists, on the other hand, believed obedience to God’s law was the only way of salvation. To them, Paul exalted righteousness out of one side of his mouth, while in reality giving license to sin out of the other side. They accused Paul of condoning lawlessness in the name of God’s grace. The doctrine of grace has always been subject to that false charge, which the apostle first answers in the first half of chapter 6. But because the misunderstanding was so common and the issue so critical, he gives the answer again from a slightly different perspective. The doctrine of salvation by God’s grace, working only through man’s faith and apart from any works, is the furthest thing from a license to sin." (MacArthur, J: Romans 1-8. Chicago: Moody Press) (Bolding added)

Ray Stedman writes:

I know that many experience this. We discover the joy of deliverance. Then we also discover that the old life still has power to tempt us and draw us back into its control. We realize that, even though it is true that Jesus Christ lives within us to be all that he is (which is all that we need), nevertheless the temptation is to strike a balance and work out a compromise. We find ourselves wanting to draw on Christ for the power to meet the times of stress that come -- the big problems -- but we rather like to put on the old comfortable slippers of the flesh the rest of the time, and enjoy that. (Click full sermon Choose Your Master)

Albert Barnes sums up Paul's question with the following thought...

The apostle proceeds to notice an objection which might be suggested. “If Christians are not under the law, which forbids all sin, but are under grace, which pardons sin, will it not follow that they will feel themselves released from obligation to be holy? Will they not commit sin freely, since the system of grace is one which contemplates pardon, and which will lead them to believe that they may be forgiven to any extent?” This Consequence has been drawn by many professing Christians; and it was well therefore, for the apostle to guard against it. (Albert Barnes' Notes on the Bible - 1798-1870)

Adam Clarke writes...

Shall we abuse our high and holy calling because we are not under that law which makes no provision for pardon, but are under that Gospel which has opened the fountain to wash away all sin and defilement? Shall we sin because grace abounds? Shall we do evil that good may come of it? This be far from us!

John Gill comments that...

"...here the apostle meets with an objection of the adversary, saying, that if men are not under the law, and are free from all obligation to it, then they may live as they list; nor can they be chargeable with sin, or that be objected to them; since where there is no law, there is no transgression, and sin is not imputed where there is no law; and if they are under grace, or in the love and favour of God, from which there is no separation, then they cannot be damned, do what they will: but this objection proceeds upon a mistaken sense of the phrase, "under the law"; for believers, though they are not under the law as the ministry of Moses, yet they are under it, as it is in the hands of Christ; and though not under its curse, yet under obligation to obedience to it, from principles of love and grace; and a transgression of it is sin in them, as in others; and which is taken notice of by God, and visited with stripes in a Fatherly way (see Hebrews 12:5-11), though His lovingkindness is not removed and to argue from the unchangeableness of God's grace, or the doctrines of it, as encouraging licentiousness, is greatly to abuse the grace of God, and manifestly betrays such persons to be ignorant of it and its influence; since nothing more powerfully engages to a love of holiness, and hatred of sin; wherefore the apostle, answers to this objection in his usual way, God forbid; signifying his abhorrence of everything of this kind." (John Gill's Exposition of the Entire Bible -1690-1771) (Bolding added)

MAY IT NEVER BE: me genoito (3SAMO):

Paul gives the same clear denial he gave in Romans 6:2. (Click exposition) As in that verse, Paul's refutation is “No, a thousand times no!”

The suggestion that God’s grace grants a license to sin is absurd. Why? Because God bestows His grace in order to free men from bondage to the power of Sin. It would be illogical for the very force that frees us from the power of Sin to at the same time re-energize the power of Sin! Grace clearly does not condone or justify continuing in sin because grace transforms the life that is saved. There is a practical application - If a person's life that gives no evidence of moral and spiritual transformation, they are exhibiting no no obvious evidence of salvation and need to carefully examine the gospel they have believed.

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ILLUSTRATIONS OF BIBLE TRUTH by Harry A. Ironside - LAW AND GRACE -  "We are not under the law, but under grace" (Ro 6:15).

Romans 6:16-19 describes the new subjection to righteousness by which grace displaces the old subjection to sin.

Do you not know - Paul speaks of a self-evident truth, the truth that when one accepts servitude to another, that enslavement becomes binding and forbids divided allegiance or servitude! Paul then proceeds to introduce us to the two different "masters", personified as Sin and Obedience.

Know (1492) (eido) (perfect tense) means absolute, positive, beyond a peradventure (chance) of a doubt, knowledge. It means to perceive intuitively and describes a self-evident truth. Paul's question is clearly rhetorical (asked merely for effect with no answer expected) and implies that his readers would readily acknowledge the truth of what he was about to say if they gave it the least thought - it is a dictate of common sense.

Present (3936) (paristemi from para = near, beside + histemi = place, set) (Click for discussion of paristemi) literally means to place or set beside or near and hence to place at someone's disposal. Paristemi means to present oneself for service or to put at the service of (sometimes translated "help" as in Romans 16:2 see note). Paristemi is in the present tense indicates this reflects the habit of one's life. The active voice represents the action as being accomplished by the subject and indicates the willing choice of obedience to a master which makes Paul’s point even more obvious.

Slaves (1401) (doulos from deo = to bind) (Click for word study of doulos) describes one who is in bondage or bound to another, in the state of being completely controlled by someone or something and a slave in the sense of being the property of the owner

Obedience (5218) (hupakoe [word study] from hupó = agency or means, under + akoúo = physical hearing and apprehension of something with the mind) means literally means "hearing under", that is, listening from a subordinate position in which compliance with what is said is expected and intended.  Hupakoe speaks of the one hearing as being under the authority of some one else. Thus, hupakoe comes to mean compliance (disposition to yield to another) with the demands or requests of someone over us. The idea of to hear under pictures subordinating one’s self to the person or thing heard and hence means “to obey” or to hearken (give respectful attention) Obedience is submission or hearkening to a command. Obedience is the carrying out the word and will of another person, especially the will of God.

You know that in effect there is no middle ground between being a slave to sin and a slave to obedience to God. Jesus clearly taught that

“No one can serve two masters" (Mt 6:24-note; Luke 16:13).

Those who are afraid of grace insist that it gives license for sinning. Paul meets this error head-on by asking the question, then flatly denying it. We are free from the law but not lawless. Grace means freedom to serve the Lord, not to sin against Him.

As Paul used the figure of slavery to illustrate death to sin and resurrection to new life in Christ and not in sin, so now he uses slavery against the idea of occasional lapses into sin. Loyalty to Christ will not permit occasional crossing over to the other side to Satan's line.

William Newell sums this section up writing...

"the answer to the second question is: God has set believers free, to serve Himself. The only other master is sin. And bondage to sin results from serving sin. But the Word of God says to the believer. Ye are not under law, but under grace." (Wuest, K. S. Wuest's Word Studies from the Greek New Testament: Studies in the Vocabulary of the Greek New Testament: Grand Rapids: Eerdmans)

YOU ARE SLAVES OF THE ONE WHOM YOU OBEY EITHER OF SIN RESULTING IN DEATH OR OF OBEDIENCE RESULTING IN RIGHTEOUSNESS: eis dikaiosunen douloi este (2PPAI) ho hupakouete (2PPAI) etoi hamartias eis thanaton e hupakoes: (Ro 6:12,17,19, 20, 21, 22, 23)

Slaves (1401) (doulos [word study] from deo = to bind) (Click additional notes on doulos) in Paul's day were those individuals who were bound to their master in servitude. Doulos in Paul's writings thus conveys the picture of a slave's close, binding tie with their master, of belonging solely to him and of being obligated to and desiring to do his will. In sum, the will of the doulos is completely consumed in the will of the master. 

Obey (5219) (hupakouo [word study] from hupó = = agency or means, under + akoúo  physical hearing and apprehension of something with the mind - akouo gives us our English acoustics - the science of design which helps one hear) literally means to listen under with attentiveness and to respond positively to what is heard. The sense is that one understands and responds accordingly. Note that hupakouo implies an inward attitude of respect and honor, as well as external acts of obedience.  Obedience on the part of children consists in listening to the advice given by parents. For example in Genesis 22 Isaac's willingness to be offered as a sacrifice is a model of such submission.

To obey means to hear under authority and thus pictures the one hearing as being under the authority of some one else. Hupakouo means to obey on the basis of having paid attention to. So first one has to hear and then one has to make a conscious choice to submit and respond to the word (optimally, His Word of righteousness and truth) heard.

It short Paul clearly teaches that a slave hearkens or gives respectful attention to either one of two masters, Sin (and the flesh) or "Obedience" (which is made possible by God's indwelling Spirit). There is no middle ground! No place for compromise in the Christian life! Hupakouo is in the present tense indicating obedience is to be the believer's habitual practice (their direction not perfection, at least not in this present life!).

The basic picture of hupakouo is that of placing oneself under what has been heard and therefore submitting to what is heard. Sin and Obedience are here both personified as "Masters". If Sin is one's master, the result will be death of both body and soul (cp James' teaching in Jas 1:14, 15-note and thus his strong warning Jas 1:16-note). If Obedience is the master, the effect of service to this master (Obedience) will be righteousness and holiness.

Paul has a parallel thought on this basic spiritual dynamic (and the basic conflict) commanding saints to...

walk (present imperative = command to continually yield to and be empowered to conduct your life in general) by the Spirit (What is the "promise" coupled with obedience to this command?), and you will not carry out the desire of the flesh (Note the order of the godly "walk": Submission to Spirit is first, not "trying" to control the desires of the flesh, as by keeping a list of "do's and don'ts" - that's putting yourself under the law! See what happens when you do that - Ro 7:5-note) for the flesh sets its desire (epithumia) against the Spirit, and the Spirit against the flesh; for these are in opposition to one another, so that you may not do the things that you please (which means every believer, as we all know too well [!], still possesses the latent desire to do "our will" rather than God's will, especially when we are bombarded by the tempting "arrows" of the world, the flesh and the devil). (Gal 5:16-note; Gal 5:17-note)

To summarize, every person is a bondservant to someone or something. Before we were saved, we were slaves of Sin. Now that we belong to Christ, we are freed from that old slavery and made servants of Christ.

Righteousness (1343) (dikaiosune [word study] from dikaios [word study] = being proper or right in the sense of being fully justified being or in accordance with what God requires) is the quality of being upright. In its simplest sense dikaiosune conveys the idea of conformity to a standard or norm. In this sense righteousness is the opposite of hamartia (sin), which is defined as missing of the mark set by God. In this sense righteousness is the opposite of hamartia (sin), which is defined as missing of the mark set by God.

Dikaiosune is rightness of character before God and rightness of actions before men.  Righteousness of God could be succinctly stated as all that God is, all that He commands, all that He demands, all that He approves, all that He provides through faith in Christ (Click here to read Pastor Ray Pritchard's interesting analysis of righteousness in the Gospel of Matthew).

What's Paul's point? Who do you habitually obey? A person’s general pattern of living proves who one's true master is. If a person's life is characterized continually by sin (as a lifestyle), then that person is a slave to Sin (as a Master). If one's life is characterized by habitual (Paul did not say "perfect"!) obedience),  then that person is demonstrating by their habitual conduct that they are a slave to the Lord Jesus Christ. The end result of the first slavery is both physical and spiritual death, whereas that of the second slavery is righteousness (right attitudes and actions before God and men), the mark of eternal life. The habitually unrighteous life cannot be a Christian life.

Matthew Henry sums it up well stating that...

If we would know to which of these two families we belong, we must inquire to which of these two masters we yield our obedience.

William MacDonald adds that...

Sin’s slaves are bound by guilt, fear, and misery, but God’s servants are free to do what the new nature loves. So why be a slave when you can be free? (MacDonald, W., & Farstad, A. Believer's Bible Commentary: Old and New Testaments. Nashville: Thomas Nelson)

William Newell writes that...

Let us remember then, that the obedience unto righteousness of Ro 6:16, is "the obedience of faith, " always.

Comment: In other words, dear believer, Newell is saying we are to walk by faith, not sight. The order is first "Trust" and then "Obey" for there's no other way to be happy in Jesus than to...

Trust and Obey
When we walk with the Lord in the light of His Word,
What a glory He sheds on our way!
While we do His good will, He abides with us still,
And with all who will trust and obey.

Trust and obey, for there’s no other way
To be happy in Jesus, but to trust and obey.

Moule reminds us that

in the very act of leaving (as the result of God's actions in our heart) the bond-service of Sin you entered that of Pardon as taught in the Gospel, and are thus bound to obey as much as ever, though in the opposite direction. (The Epistle of Paul the Apostle to the Romans - Online)

If one manifests no inclination and/or no power to be obedient to the Lord Jesus Christ, then they need to examine themselves in light of Paul's serious warning to...

Test (peirazo - present imperative = Continual command because this is a continual need all of us! See the attitude we must all continually have in 1Co 10:12) yourselves (This pronoun is first in the Greek sentence for emphasis! Quit judging others! Quit looking at others and using their disobedience to justify your disobedience as "not so bad"!) to see if you are in the faith; examine (dokimazo = present imperative) yourselves! Or do you not recognize this about yourselves, that Jesus Christ is in you-- unless indeed you fail the test (adokimos = that  which does not prove itself to be such as it ought to be and which is therefore disapproved and useless!)? (2Corinthians 13:5)

C H Spurgeon phrases it this way...

If you are doing the deeds of sin, you are the servants of sin and only as you are doing the will of God can you claim to be the servant of God. “Hereby we know that we know him, if we keep His commandments.” (1Jn 2:3) That becomes the index of our condition. The man, then, that lives in sin and loves it, need not talk about the grace of God to which he is a stranger, for the mark of those that come under grace is this, that they serve God, and no longer serve sin. (Spurgeon on Romans)

BUT THANKS BE TO GOD THAT THOUGH YOU WERE SLAVES OF SIN : charis de to theo hoti ete (2PIAI) douloi tes hamartias: (Ro 1:8; 1Chr 29:12, 13, 14, 15, 16; Ezra 7:27; Mt 11:25,26; Acts 11:18; 28:15; 1Co 1:4; Ep1:16; Phil 1:3, 4, 5; Col 1:3,4; 1Th 1:2,3; 3:9; 2Th 1:3; 2Ti 1:3, 4, 5; Philemon 1:4; 2Jn 1:4; 3Jn1:3) (1Cor 6:9, 10, 11; Ep 2:5, 6, 7, 8, 9, 10; 1Ti 1:13, 14, 15, 16; Titus 3:3, 4, 5, 6, 7; 1Pe 2:9; 4:2, 3, 4, 5)

Be cautious relying completely on paraphrase translations, which are less faithful to the original Greek (or Hebrew) (Click for comparison of different translations). Paraphrases may help understand the text but can also be misleading as is the The Living Bible translation, which reads...

"Thank God that though you once chose to be slaves of sin..." (Bolding added)

This statement is not theologically accurate! Everyone born has been born into Adam (Ro 5:12-note) and did not have a choice to obey sin or not. As Paul has clearly taught, Sin is the Master of all who are unsaved. The unregenerate person (Jn 3:3, 5) is under the control of Sin and this is the position of the natural man, without exception. No matter how outwardly moral, upright, or benevolent an unsaved person’s life may be, all that he thinks, says, and does emanates from a proud, sinful, ungodly heart (Ro 3:10-note).

But - This conjunction should always alert the attentive reader that the writer is introducing a change of direction. So Paul begins a contrast which expresses the absolute incompatibility of living in sin on the part of the believer.

Thanks be (5485) (charis) reads more literally "grace to God". Paul moves from the principle in the preceding verse (Ro 6:16) to the experience of the Roman believers. The apostle’s gratitude to God lies in the fact that their former condition is a thing of the past and his believing readers are no longer subject to that slavery which leads to death.

Were (imperfect tense) signifies an action being committed over and over, which reflects the reality of the unregenerate person, who is under the continual slavery to Sin.  The imperfect tense indicates that slavery was an ongoing reality before the new birth (but now = Ro 6:11NLT-note)

YOU BECAME OBEDIENT FROM THE HEART TO THAT FORM OF TEACHING TO WHICH YOU WERE COMMITTED: hupekousate (2PAAI) de ek kardias eis on paredothete (2SAPI) tupon didaches eis on paredothete (2SAPI):: (Ro 1:5; 2:8; 15:18; 16:26; Ps 18:44; 2Cor 10:5,6; Heb 5:9; 11:8; 1Pet 1:22; 3:1; 4:17) (2Ti 1:13)

Peter has a parallel description (and exhortation) writing to the believers who were undergoing persecution and testing times...

Since you have in obedience to the truth (the Gospel - cp Col 1:5-note) purified your souls for a sincere (anuopkritos) love of the brethren (philadelphia), fervently love (agapao in the aorist imperative) (Truth transforms our mind and heart so that we can carry out this new quality of love) one another from the heart, for you have been born again (anagennao) not of seed which is perishable but imperishable, that is, through the living and abiding word of God (See Power of God's Word). (1Pe 1:22, 23-note)

You became obedient (5219)  (hupakouo [word study] from hupó = = agency or means, under + akoúo  = physical hearing and apprehension of something with the mind) literally means to listen under with attentiveness and to respond positively to what is heard. It means to hearken or give respectful attention to. Hupakouo is in the aorist tense which points to an action which has been completed at a definite time in the past. What time? Clearly, when they believed the life giving Gospel of the grace of God (Acts 20:24). The Roman Christians had given wholehearted obedience to the gospel to which they had been committed, including all the doctrines Paul taught in the book of Romans. Now they possessed a new nature which enabled them to obey their new master, the Lord Jesus Christ.

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Redeemed - Among the many names given to our Lord in the Bible, one is especially dear to me. It is the name Redeemer. The word redeem literally means "to buy back." It suggests that something has been sold or forfeited in order to pay a debt. When the price of its redemption has been paid, the lost article can be reclaimed.

Man was created in God's image, but he sold out to Satan for some fruit from a forbidden tree. Since that time, all mankind has been enslaved to sin and under judgment. The purchase price of redemption was the sacrificial death of Jesus Christ, which met the demands of God's holiness. Everyone who accepts God's gift of forgiveness is set free and becomes a slave of Christ the Redeemer (Ro 6:22).

Many years ago, a man visited a slave market. He watched for a while, then bid on a slave until no one was able to go any higher. After paying the price, he gave the bill of sale to the slave, and said, "I have purchased you to set you free." Overcome with gratitude, the slave refused to leave him and became his devoted servant for life.

Jesus paid an enormous price for our salvation. Do we serve Him out of gratitude? — M. R. De Haan (Our Daily Bread, Copyright RBC Ministries, Grand Rapids, MI. Reprinted by permission. All rights reserved)

My new life I owe to Thee,
Jesus, Lamb of Calvary;
Sin was canceled on the tree,
Jesus, blessed Jesus. --Blanchard

Jesus gave his all for us--
Are we giving our all for Him? (Ro 6:17)

From the heart - Not just the "head" but from our "control center" (see below). Paul is describing more than intellectual acceptance and obedience. He is saying that the believer's new obedience comes from deep within, from their new heart which is indwelt by a new power (see Ezekiel 36:26, 27, cp Ezek 11:19, 18:31, Dt 30:6,  Jer 31:33, 32:39, 40).

Heart (2588) (kardia) does not refer to the physical organ but is always used figuratively in Scripture to refer to the seat and center of human life. The heart is the center of the personality, and it controls the intellect, emotions, and will.  No outward obedience is of the slightest value unless the heart turns to God.

Kardia is used 158 times in the NAS - Mt 5:8, 28; 6:21; 9:4; 11:29; 12:34, 40; 13:15, 19; 15:8, 18, 19; 18:35; 22:37; 24:48; Mk. 2:6, 8; 3:5; 6:52; 7:6, 19, 21; 8:17; 11:23; 12:30, 33; Lk 1:17, 51, 66; 2:19, 35, 51; 3:15; 5:22; 6:45; 8:12, 15; 9:47; 10:27; 12:34, 45; 16:15; 21:14, 34; 24:25, 32, 38; Jn 12:40; 13:2; 14:1, 27; 16:6, 22; Acts 2:26, 37, 46; 4:32; 5:3, 4; 7:23, 39, 51, 54; 8:21, 22; 11:23; 13:22; 14:17; 15:9; 16:14; 21:13; 28:27; Ro 1:21, 24; 2:5, 15, 29; 5:5; 6:17; 8:27; 9:2; 10:1, 6, 8, 9, 10; 16:18; 1Co. 2:9; 4:5; 7:37; 14:25; 2 Co. 1:22; 2:4; 3:2, 3, 15; 4:6; 5:12; 6:11; 7:3; 8:16; 9:7; Ga 4:6; Ep 1:18; 3:17; 4:18; 5:19; 6:5, 22; Php 1:7; 4:7; Col 2:2; 3:15, 16, 22; 4:8; 1Th 2:4, 17; 3:13; 2Th 2:17; 3:5; 1Ti 1:5; 2Ti 2:22; He 3:8, 10, 12, 15; 4:7, 12; 8:10; 10:16, 22; 13:9; Jas. 1:26; 3:14; 4:8; 5:5, 8; 1Pe 1:22; 3:4, 15; 2Pe 1:19; 2:14; 1Jn 3:19, 20, 21; Re 2:23; 17:17; 18:7. NAS = kardia as heart, 102; heart's, 1; hearts, 49; mind, 2; minds, 1; quick, 1; spirit, 1.  Kardia gives us the English cardiac and similar terms.

Hughes explains that what Paul is saying here is that...

"The heart is the wellspring of man’s spiritual life, and that is where the Roman Christians’ obedience was rooted. It was not just a formal obedience—it came from the center of their being. This is the example of slavery Paul holds up for us all: a heartfelt obedience to Christ and his Word. It is an obedience which brings liberation." (Hughes, R. K. Romans: Righteousness from heaven. Preaching the Word. Wheaton, Ill.: Crossway Books)

While kardia does represent the inner person, the seat of motives and attitudes, the center of personality, in Scripture it represents much more than emotion, feelings. It also includes the thinking process and particularly the will. For example, in Proverbs we are told, “As (a man) thinks in his heart, so is he” (Proverbs 23:7). Jesus asked a group of scribes, “Why are you thinking evil in your hearts?” (Matthew 9:4). The heart is the control center of mind and will as well as emotion.

The Scottish writer John Eadie says that...

The “heart” belongs to the “inner man,” is the organ of perception as well as of emotion; the centre of spiritual as it is physically of animal life.

Vine writes that kardia...

"...came to denote man’s entire mental and moral activities, and to stand figuratively for the hidden springs of the personal life, and so here signifies the seat of thought and feeling." (Vine, W. Collected writings of W. E. Vine. Nashville: Thomas Nelson )

MacArthur commenting on kardia writes that...

"While we often relate heart to the emotions (e.g., “He has a broken heart”), the Bible relates it primarily to the intellect (e.g., “Out of the heart come evil thoughts, murders, adulteries, fornications, thefts, false witness, slanders,” Matt 15:19). That’s why you must “watch over your heart with all diligence” (Proverbs 4:23). In a secondary way, however, heart relates to the will and emotions because they are influenced by the intellect. If you are committed to something, it will affect your will, which in turn will affect your emotions." (Drawing Near. Crossway Books) MacArthur adds that "In most modern cultures, the heart is thought of as the seat of emotions and feelings. But most ancients—Hebrews, Greeks, and many others—considered the heart to be the center of knowledge, understanding, thinking, and wisdom. The New Testament also uses it in that way. The heart was considered to be the seat of the mind and will, and it could be taught what the brain could never know. Emotions and feelings were associated with the intestines, or bowels." (MacArthur, J: Ephesians. 1986. Chicago: Moody Press)

Like our heart it denotes the seat of feeling as contrasted with intelligence. 2Cor 2:4; Romans 9:2  (note); Ro 10:1 (note); 2Cor 6:11; Philippians 1:7 (note). But it is not limited to this. It is also the seat of mental action, feeling, thinking, willing.

1. Of intelligence, Romans 1:21 (note) 2Cor 3:15; 4:6; Ep 1:18 (note).

2. Of moral choice, 1Cor 7:37 2Cor 9:7.

3. As giving impulse and character to action, Romans 6:17 (note); Ephesians 6:5 (note); Col 3:22 (note); 1Ti 1:5; 2Timothy 2:22 (note) . The work of the law is written on the heart, Ro 2:15 (note). The Corinthian Church is inscribed as Christ’s epistle on hearts of flesh, 2Cor 1:23.

4. Specially, it is the seat of the divine Spirit, Gal 4:6; Romans 5:5 (note); 2Cor 1:22. It is the sphere of His various operations, directing, comforting, establishing, etc., Php 4:7 (note); Col 3:15 (note); 1Th3:13 (note); 2Th 2:17; 3:5. It is the seat of faith, and the organ of spiritual praise, Ro 10:9 (note); Acts 2:42 Ephesians 5:19 (note); Colossians 3:16 (note).

It is equivalent to the inner man, Ep 3:16 (note); Ep 3:17 (note). Its characteristic is being hidden, Ro 2:28, 29 (note); Ro 8:27 (note); 1Cor 4:5; 14:25.

It is contrasted with the face, 1Th 2:17 (note); 2Cor 5:12; and with the mouth, Ro 10:8 (note).

The phrase "became obedient from the heart" is important. Paul's point is that God works His salvation in a person's innermost being, changing the heart of every sinner who places their trust into Christ's finished work on Calvary. Now in a believer obedience is not forced or legalistic, but is willing. The corollary is that a person whose heart has not been changed and does not possess this desire to obey has not been saved.

Robert Haldane adds that...

Christian obedience is obedience from the heart, in opposition to an obedience which is by constraint. Any attempt at obedience by an unconverted man, is an obedience produced by some motive of fear, self–interest, or constraint, and not from the heart. Nothing can be more convincing evidence of the truth of the Gospel than the change which, in this respect, it produces on the mind of the believer. Nothing but almighty power could at once transform a man from the love of sin to the love of holiness.  (Haldane, R. An Exposition of Romans - Online) (Bolding added)

Form (5179) (tupos [words study]) properly means a "model" or "pattern" or "mold" into which clay or wax was pressed, that it might take the figure or exact shape of the mold. The word "form" is generally used to denote a resemblance between something present and something future.

The gospel is the pattern. Tupos refers to a mold such as a craftsman would use to cast molten metal. Paul’s point is that God pours His new children into the mold of divine truth. New believers now have an innate and compelling desire to know and obey God’s Word.

Robert Haldane adds that tupos...

is a reference to melted metals transferred to a mold, which obey or exactly conform to the mold. It is perhaps as probable that the reference is to wax or clay or any soft matter that takes the form of the stamp or seal. (Haldane, R. An Exposition of Romans - Online)

Jamieson commenting on form writes that...

"The idea is, that the teaching to which they had heartily yielded themselves had stamped its own impress upon them." (Jamieson, R., Fausset, A. R., Fausset, A. R., Brown, D., & Brown, D. A Commentary, Critical and Explanatory, on the Old and New Testaments)

Teaching (1322) (didache [word study]) sometimes means manner of teaching but in the present context, speaks of the content of teaching.  In didache, we have incorporated the authority of that which is taught. In the context of Romans "teaching" would refer to the Gospel"

Note that the KJV translation "doctrine was delivered you" is not accurate to the original Greek. J B Phillips more accurately conveys the meaning of the Greek writing that the readers had "honestly responded to the impact of Christ's teaching when you came under its influence." (see additional explanatory note below).

Were committed (3860) (paradidomi [word study] from para = alongside, beside + didomi = give) means to hand over to or to give over into (one’s) power. Paradidomi involves either the handing over of a presumably guilty person for punishment by authorities or the handing over of an individual to an enemy who will presumably take undue advantage of the victim.

William Newell elaborates on what it means to be committed to the teaching...writing...

Note that the Old Version misses the entire sense of this seventeenth verse in translating: "that form of doctrine which was delivered unto you, " whereas the true rendering is, that form of doctrine unto which ye were handed over (or, delivered). For the verb (paradidomi) is in the plural--ye were delivered over! This statement instructs us deeply in the Divine arrangements. The Israelites, for example, were delivered over to Moses and the Law. It was not only that the Law was delivered by Moses to them; they were them- selves delivered over to a legal dispensation--to a "mold of doctrine, " which had the Ten Commandments as the foundation, and the "ten thousand things of the Law" spoken in accordance therewith. The Jews knew they were under the Law. They had been handed over to it, to its demands, and to its whole economy. Likewise, believers now are delivered over to a form or pattern of teaching. Summarily, this is the Gospel, --particularly, the work of Christ on the cross. Believers have been handed over by God to the mighty facts, not only that their guilt was put away on the cross, but that they, as connected with Adam, died with Christ; that their history in Adam is thus entirely ended before God; and that they now share the risen life of Christ, and are before God as risen ones (Romans 6:10,11). And all believers are comprehended in these great truths, whether they apprehend them or not! It is the first duty of every teacher of God's saints to open to them the glorious facts already true about them, and unto which great mold or form of doctrine, they have been "delivered over" by God." (Romans 6)

Kenneth Wuest agrees with Newell and sums up the meaning of this verse...

It is true that according to the authorized version., the doctrines of salvation were delivered to us, and we by the grace of God believed them. However, that is not what Paul said in his Greek. The verb “delivered” is second person plural. The Greek text reads, “the form of doctrine into which you were delivered.” That is, in salvation, God constituted the believer according to this chapter (vv. 1–14) inwardly so that he would react to the doctrines of grace by nature (the divine nature) in such a way as to receive and obey them. We were delivered into the teaching (doctrine - didache) in that we were constituted in salvation so that we would obey it. Paul thanks God that whereas before salvation we were slaves of the evil nature, we were in salvation delivered (handed over - paradidomi) to the teachings of grace so that we become slaves of righteousness. (Wuest, K. S. Wuest's Word Studies from the Greek New Testament: Studies in the Vocabulary of the Greek New Testament: Grand Rapids: Eerdmans)

Witness Lee, founder of the Local Church movement, wrote a book entitled "Christ Versus Doctrine", the main thesis of which is that it is a personal relationship to Christ that matters and that doctrine actually interferes with that relationship. The book not only is unbiblical but, as one might guess from the title, is also self-contradictory. Doctrine is simply another word for teaching, and the purpose of Lee’s book, of course, was to teach his own doctrine.

God has so constituted us inwardly as believers (according to Ro 6:1-14) that we would react to the doctrines of grace by nature (the divine nature that now indwells us) in such a way as to hear, to receive and to obey them.

C H Spurgeon adds...

If, then, a man lives a life of sin, he proves that he is the servant of sin, for he has obeyed its commands, and let that man know assuredly that he has nothing to do with Christ while he is living in sin. But if a man lives in obedience to Christ and seeks after righteousness, and true holiness, that man is evidently the servant of righteousness, and so the servant of God.

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It is a wonderful heart-searching text, is this: let us put ourselves under its power. Whatever you obey, that is your master: and if you obey the suggestions of sin, you are the slave of sin: and it is only as you are obedient to God that you are truly the servants of God. So that, after all, our outward, walk and conversation are the best test of our true condition. Without holiness no man shall see the Lord, nor can (He 12:14-note) he have any reason to believe that he belongs to God. (Spurgeon on Romans)