We were - Is in the imperfect tense, indicating over and over, again and again we were foolish. Believers need to continually remember wherefrom they have come by virtue of the supernatural grace of God. As Spurgeon once put it...

No man here has any idea of how bad he really is. You do not know how good the grace of God can make you, nor how bad you are by nature, nor how bad you might become if that nature were left to itself.

The first words of this verse are "we were" placed emphatically at the beginning of this description of unregenerate man to emphasize that this was the state of every believer (including Paul himself) before Christ came into their life. The foot of the Cross is level footing for everyone. As Spurgeon puts it...

Well, then, if other people are foolish, we ought to bear with them.

For (whenever you see a "for" always ask "What's it there for?") is the Greek conjunction gar (which usually introduces an explanation or the reason for a statement which precedes) and in this case explains the reason for the right conduct Paul has just prescribed in the preceding section.

Expositor's Bible Commentary summarizes this section noting that Paul

now "advances three supporting motives: their own pre-Christian past (v3), the saving work of God in believers (v4-8a), and the necessary connection between Christian truth and conduct (v8b). (Gaebelein, F, Editor: Expositor's Bible Commentary 6-Volume New Testament. Zondervan Publishing)

Note that the NIV omits the conjunction "for" and is another reason a more literal version like NAS or NKJV is preferable for serious Bible study.

W E Vine comments that

"the remembrance of the fact that we once manifested some of these characteristics of our unregenerate nature, should in itself be an incentive to us to fulfill the exhortations just given. We ourselves stood in need of kindness, gentleness, meekness, on the part of others, and were so treated by God in His long-suffering. How then can we refuse kindness to those who stand in need of it?" Vine goes on to write that "Foolishness is evidence of a blunted mind; disobedience is evidence of a hardened heart; deception is evidence of a perverted will; bondage to lusts and pleasures is evidence of a carnal mind; malice and envy and hate are proofs of selfishness, pride and grasping ambition. And all are the effects of sin." (Vine, W. Collected writings of W. E. Vine. Nashville: Thomas Nelson ) (Bolding added)

Thomas Constable writes that

"to motivate his readers to obey these commands (Ed note: those instructions in the preceding verses) Paul encouraged them by reminding them of the way they used to be. They had already come a long way. Each characteristic he mentioned in this verse contrasts with one he had urged his readers to adopt earlier in this epistle. They—Paul included himself—had been foolish, not sensible; disobedient, not submissive; deceived, not enlightened; and enslaved, not free and self-disciplined. Moreover they had been malicious, not peaceable; envious, not considerate; and hateful, not loving."

EBC writes that...

"The remembrance of our own past should be a powerful motive for gentleness and consideration toward the unsaved...It is salutary to remember our own past moral condition when dealing with the unsaved in their degradation. The picture of our past is vividly and concisely drawn." (Gaebelein, F, Editor: Expositor's Bible Commentary 6-Volume New Testament. Zondervan Publishing)

Keathley adds that

"In these verses we see the truth that, as George Whitefield so accurately put it when he saw a criminal going to the gallows, “there but for the grace of God go I.”...The tendency is to become pharisaic and look down on those whose lifestyle is not like ours. There should be a moral difference, but the issue is not the moral difference, rather the cross is what made the difference. To stress this, Paul uses terms to stress the change. The “for we too were once” of verse 3 must be seen in the light of “but when the kindness of God appeared.” But for the grace work of God, we would still be in the same predicament as the unbelieving world, a predicament graphically described by the apostle."

Paul has a similar commentary on humanity's state outside of Christ writing that...

We also once "were (spiritually) dead in (our) trespasses and sins, in which (we) formerly walked according to the course of this world (under the sway of the tendency of this present evil age), according to the prince of the power of the air, of the spirit that is now working in the sons of disobedience (unwilling to be persuaded, obstinate, rebellious, unbelieving, striving continually against the purposes of God) Among them we too all formerly lived in the lusts of our flesh (our behavior governed by our corrupt and sensual nature), indulging the desires of the flesh and of the mind, and were by nature children (born with a sinful nature inherited from Adam) of wrath (objects of God's holy hatred of sin representing His attribute of necessary antagonism to everything evil), even as the rest." (Eph 2:1-3)

Writing to the Corinthians, Paul reminded the saints (and all of us) of their former despicable, degraded, debased, despairing condition --

"Or do you not know that the unrighteous shall not inherit the kingdom of God? Do not be deceived; neither fornicators, nor idolaters, nor adulterers, nor effeminate, nor homosexuals, nor thieves, nor the covetous, nor drunkards, nor revilers, nor swindlers, shall inherit the kingdom of God. And such were some of you; but you were washed (purified by a complete atonement for sin and made free from the guilt of sin), but you were sanctified (set apart from the world unto God), but you were justified (declared righteous on the basis of your faith in the gospel) in the name of the Lord Jesus Christ, and in the Spirit of our God." (1Cor 6:9-11)

Now ponder this list for a moment -- what is your reaction? Are we not benefactors of infinite mercy? Are we not recipients of so great a salvation? Are we not under obligation out of love and gratitude to serve our Master and not ourselves? Let your heart be renewed by thoughts of the fire from which you were snatched and purpose today to seek first His kingdom and His righteousness all the remaining days of your life on earth. Live for eternity and for His glory!

Remember that we also once were

"alienated (estranged from, strangers to and withdrawn from God) and hostile (active enemies of God, antagonistic toward Him) in mind (actively) engaged in evil deeds (alienation of mind showing itself in wicked works)" (see note Colossians 1:21)

Peter adds that...

"the time already past is sufficient for you to have carried out the desire of the Gentiles, having pursued a course of sensuality, lusts, drunkenness, carousals, drinking parties and abominable idolatries." (see note 1 Peter 4 :3)

We also once were just like them and would still be like them if it were not for

"the word of the cross...(which) is the power of God" (1Cor 1:18) which "delivered us from the domain of darkness and transferred us to the kingdom of His beloved Son, in Whom we have redemption, the forgiveness of sins" and daily provides the power to "walk in newness of life" (see note Romans 6:4) "no longer...slaves to (the power, rule and reign of) sin" (see note Romans 6:6).  Hallelujah!

Spurgeon writes that...

A threefold set of evils is here described. The first set consists of the evils of the mind: “We were sometimes foolish, disobedient, deceived.”

We were foolish. We thought we knew, and therefore we did not learn. Every lover of vice is a fool writ large. In addition to being foolish, we are said to have been disobedient; and so we were, for we forsook the commands of God. We wanted our own will and way. We were unwilling to yield God His due place either in providence, law, or gospel. Paul adds that we were deceived, or led astray. We were the dupes of custom and of company. We were here, there, and everywhere in our actions: no more to be relied upon than lost sheep.

Foolish (453) (anoetos from a = without + noéo = comprehend) means literally “not having a mind”, and so pictures the unsaved as without spiritual understanding, ignorant of God and continually manifesting an unwillingness to use their mental faculties to understand the truth about God. They clearly did not lack intelligence but did lack godly wisdom. They lacked discernment of spiritual realities, having become

darkened in their understanding, excluded from the life of God, because of the ignorance that is in them, because of the hardness of their heart. (see note Ephesians 4:18).

Elsewhere Paul describes says

a natural man does not accept the things of the Spirit of God; for they are foolishness to him, and he cannot understand them, because they are spiritually appraised. (1Cor 2:14)

What a play on words -- "foolishness" to him who is the real "fool".

By using the word foolish, Paul is saying that, no matter how advanced one might be in education and intellectual accomplishments, if he or she refuses to recognize God and trust in Him for deliverance from the penalty of sin which is death, they are foolish concerning the most important truth in all eternity. God's attitude towards the foolish is expressed in Proverbs, Solomon asking the question

"How long, O naive ones, will you love simplicity? And scoffers delight themselves in scoffing, and fools hate knowledge? (note now the riches of God's kindness and forbearance and patience in beckoning to all men to) Turn to My reproof, behold, I will pour out My Spirit on you. I will make My Words known to you." (Pr 1:22,23)

Paul adds that

"since in the wisdom of God the world through its wisdom did not come to know God, God was well-pleased through the foolishness of the message preached (Christ crucified...the power of God and the wisdom of God) to save those who believe."(1Cor 1:21-24)

Paul Johnson in his book  Intellectuals documents the morass of unspeakable moral filth and ungodliness that has characterized most of the leading intellectual architects of modern Western culture. Their astounding mental capacities and their profound impact on modern society are indisputable and yet they are the very ones Paul is describing in this section for they “did not see fit to acknowledge God (or even to consider Him worth knowing!)" and therefore they were judicially given over by God

"to a depraved mind (literally one that is worthless and rejected by God for it is base, perverted, corrupted, debauched, warped, twisted, degenerate) to do things not proper or decent but loathsome" (see note Romans 1:28).

To study the biographies of the great "movers and shakers" of history is to study the height and depth of despicable degradation and depravity of which men originally made in God's image are capable! A brilliant mind is imminently capable of even the most heinous evil. Witness the appalling, unspeakable atrocities of Nazi Germany, which were conceived and perpetrated by brilliant men in arguably the most intellectually, scientifically and culturally advanced nation of modern times.

Disobedient, deceived, enslaved - Spurgeon comments...

DISOBEDIENT: apeitheis:  (Mt 21:29; Acts 9:1-6; 26:19,20; Eph 2:2; 1Pet 1:14)

Disobedient (545) (apeithes  from a = without + peítho = persuade) (See studies on related words apeitheia; apeitheo) literally describes one who refuses to be persuaded (unpersuadable), thus picturing one who willfully disregards authority. Impersuasible, incompliant, contumacious.

In studying apeithes it is important to understand that the stem peith- (pith-, poith-) has the basic meaning of trust (cf. Latin = fido, fides; English = fidelity). Trust can refer to a statement, so that it has the meaning to put faith in, to let oneself be convinced, or to a demand, so that it gets the meaning of obey, be persuaded. The active meaning of the verb stem peith- then is to convince and persuade and is especially characteristic of Greek thought. In secular Greek it interesting to note that "Peitho" (art of persuading) was even regarded as a goddess! (see Brown, Colin, Editor. New International Dictionary of NT Theology. 1986. Zondervan)

Apeithes pictures a stubborn, stiff-necked attitude and speaks of disbelief manifesting itself in disobedience. Apeithes is opposed to pistis or belief (trust). 

TDNT says apeithes...

means “unworthy of belief,” then “disobedient.”

In the present context apeithes describes the person who refuses obedience to God, resisting His Word and remains steadfastly rebellious against God's natural laws and those which human society requires.

Paul describes a progression is from an unwillingness to use one's mental faculties (foolish) in order to understand the truth about God and His glorious gospel, in turn and inevitably leading to an unwillingness to be persuaded by the truth. Men do not avoid the gospel of Christ because of insufficient facts but because of proud and unrepentant hearts. Such is the natural character of the human heart, Jeremiah recording that the

heart is more deceitful than all else and is desperately sick. (Jer 17:9)

Solomon wrote that

the hearts of the sons of men are full of evil, and insanity is in their hearts throughout their lives (Eccl 9:3).

Apeithes is found 6 times in the NT...

Luke 1:17 "And it is he who will go as a forerunner before Him in the spirit and power of Elijah, to turn the hearts of the fathers back to the children, and the disobedient to the attitude of the righteous; so as to make ready a people prepared for the Lord."

Acts 26:19 "Consequently, King Agrippa, I did not prove disobedient to the heavenly vision,

Romans 1:30 (note) slanderers, haters of God, insolent, arrogant, boastful, inventors of evil, disobedient to parents,

2 Timothy 3:2 (note) For men will be lovers of self, lovers of money, boastful, arrogant, revilers, disobedient to parents, ungrateful, unholy,

Titus 1:16 (note) They profess to know God, but by their deeds they deny Him, being (continually = their "lifestyle") detestable and disobedient, and worthless for any good deed.

Titus 3:3 (note) For we also once were foolish ourselves, disobedient, deceived, enslaved to various lusts and pleasures, spending our life in malice and envy, hateful, hating one another.

Apeithes is used 5 times in the non-apocryphal Septuagint (LXX) ...

Numbers 20:10 and Moses and Aaron gathered the assembly before the rock. And he said to them, "Listen now, you rebels (Hebrew = marah [04784] = be contentious or rebellious; Lxx = apeithes) ; shall we bring forth water for you out of this rock?"

Deuteronomy 21:18 "If any man has a stubborn and rebellious son who will not obey his father or his mother, and when they chastise him, he will not even listen to them,

Isaiah 30:9 For this is a rebellious (Lxx = apeithes) people, false sons, Sons who refuse to listen To the instruction of the LORD;

Jeremiah 5:23 'But this people has a stubborn and rebellious heart; They have turned aside and departed.

Zechariah 7:12 "And they made their hearts like flint (Lxx = apeithes = disobedient! Flint is a good metaphor for such a hard heart!) so that they could not hear the law and the words which the LORD of hosts had sent by His Spirit through the former prophets; therefore great wrath came from the LORD of hosts.

Jesus taught that

from within, out of the heart of men, proceed the evil thoughts, fornications, thefts, murders, adulteries, deeds of coveting and wickedness, as well as deceit, sensuality, envy, slander, pride and foolishness. (see note Matthew 7:21; 7:22)

This is who we once were outside of Christ. Paul is saying that this truth should motivate believers to treat others the way God in His grace treated us when we were involved in ungodly activities

"for while we were still helpless, at the right time Christ died for the ungodly", God demonstrating "His own love toward us, in that while we were yet sinners, Christ died for us." (see notes Romans 5:6; Romans 5:8)

DECEIVED: planomenoi (PPPMPN): (Isa 44:20; Ob 1:3; Luke 21:8; Gal 6:3; Js 1:26; Rev 12:9; 13:14)

Deceived (4105) (planao from plane which describes "a wandering" and gives us our English word "planet") means literally made to wander and so to go (active sense) or be led (passive sense as of sheep in Mt 18:12-13) astray.

Note that in this passage planao is in the passive voice which indicates an outside force or influence (e.g., the unregenerate heart in unbelievers in this context, but in other contexts referring to the power of sin rendered ineffective but unfortunately still latent in believers) is causing the deception that leads one down the wrong path. The present tense indicates the sad truth that unsaved men and women are continually being led astray from God, even to the point that they refuse to believe that in the end they will be judged by Him (cf notes Revelation 20:11; 20:12; 20:13; 20:14; 20:15).

Literal wandering is described in Hebrews 11:38 (note). Spiritual wandering is described in (1 Peter 2:25 - note) In spiritual terms, planao means to be made to err from the right way, the highway of truth and holiness. Straying in the spiritual sense occurs when one does not adhere to the truth (James 5:19) and/or forsakes the right way (see note 2 Peter 2:15)

Scripture teaches us that various things or classes of people can deceive a person including the following...

Signs, sorcery, pretenders coming in Jesus' name (Mt 24:4-5, Mark 13:5-6, Luke 21:8),

False teachers (1John 2:26, 3:7),

False Christs and false prophets (Mt 24:11,24, see note on Jezebel the false prophetess Rev 2:20),

Not  understanding the Scriptures or the power of God (Mt 22:29, Mark 12:24),

One's own self (evil flesh) ("self deception" 1 Cor 6:9, 1 Cor 15:33, Gal 6:7, see note Titus 3:3, 1 John 1:8),

One's heart (synonymous with evil flesh  - see note Hebrews 3:10)

Evil men and imposters (see note 2 Timothy 3:13),

The devil (see notes Rev 12:9, Rev 20:3; 20:8; 20:10),

Babylon (see note Revelation 18:23)

The Antichrist's false prophet (see notes Rev 13:14, 19:20)

Jesus uses planao several times to describe one who is mistaken (Matthew 22:29, Mark 12:24, 12:27)

Matthew Henry writes that

Man in this his degenerate state is of a straying nature, thence compared to a lost sheep; this must be sought and brought back, and guided in the right way, Ps 119:176. (See Spurgeon's Note) He is weak, and ready to be imposed upon by the wiles and subtleties of Satan, and of men lying in wait to seduce and mislead.

Clarke writes that deceived is

erring - wandering from the right way in consequence of our ignorance, not knowing the right way; and, in consequence of our unbelief and obstinacy, not choosing to know it.

Basically deception refers to a deliberate misrepresentation of the truth, especially in moral and spiritual matters, in order to purposely mislead another person.  In this sense, the truth can be misrepresented first of all by our own sinful heart (which is the control center of our character and our moral and spiritual life) (Jer 17:9, Hebrews 3:10 [note], Js 5:19, 1Jn 1:8), by false prophets (Jer 29:8, Mt 24:4-5, Revelation 13:14 [note]), by false teachers (Eph 5:6 [note], 2 Peter 2:14 [note], 1Jn 2:26, 1Jn 3:7, 2Jn 1:7, Jezebel Revelation 2:20 [note]) and of course especially by the ultimate "Deceiver", our old Adversary, the consummate Liar (Jn 8:44), Satan himself (see notes Revelation 12:9, 20:3, 20:8, 20:10). Satan’s objective is to deceive sinners into ever greater sin and ungodliness.

Deceivers are very good as these illustrations from Today in the Word emphasizes...

Despite the mind-numbing brutality of the Joseph Stalin regime in the Soviet Union, his propaganda machine did its job well. Many Russians hailed him as a hero and a savior, including a young school girl who was chosen to greet Stalin on one occasion. Years later, this woman recalled Stalin taking her onto his lap, smiling like a loving father. She was starry-eyed, and she cherished the moment for many years. Only later did she learn that during this period, Stalin had her parents arrested and sent to the labor camps, never to be seen again.

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In late September 1864 Confederate General Nathan Bedford Forrest was leading his troops north from Decatur, Alabama, toward Nashville. But to make it to Nashville, Forrest would have to defeat the Union army at Athens, Alabama. When the Union commander, Colonel Wallace Campbell, refused to surrender, Forrest asked for a personal meeting, and took Campbell on an inspection of his troops. But each time they left a detachment, the Confederate soldiers simply packed up and moved to another position, artillery and all. Forrest and Campbell would then arrive at the new encampment and continue to tally up the impressive number of Confederate soldiers and weaponry. By the time they returned to the fort, Campbell was convinced he couldn't win and surrendered unconditionally!

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“Marathoner Loses by a Mustache.” So read the headline of a recent Associated Press story. It appeared that Abbes Tehami of Algeria was an easy winner of the Brussels Marathon—until someone wondered where his mustache had gone! Checking eyewitness accounts, it quickly became evident that the mustache belonged to Tehami’s coach, Bensalem Hamiani. Hamiani had run the first seven-and-a-half miles of the race for Tehami, then dropped out of the pack and disappeared into the woods to pass race number 62 on to his pupil. “They looked about the same,” race organizers said. “Only one had a mustache.” It’s expected that the two will never again be allowed to run in Belgium.

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Deception has been a part of warfare since the Trojan horse. During WWII, it became high art. Members of the 23rd Headquarters Special Troops used special “weapons” like dummy planes, tanks, antiaircraft guns, and amplified recordings that created war sounds to fool the German high command. To enable a combat unit to change positions or even attack when the Germans thought it had not moved at all, the 1800 men of the 23rd impersonated entire divisions. They would move in at night, change insignias, and inflate their rubber decoys. Meanwhile, the troops they were replacing sneaked away. Such deception was a major factor in the success of the Allies’ D-Day invasion, as the German 15th Army waited elsewhere for an assault that never came.

How dangerous is deception? Dennis Heatherington explains that it could be deadly...

A person on railroad tracks hear a train approaching, looks behind him, sees the train and then freezes on the tracks in fear. The train “outruns” its sound—which means that by the time you hear it, it is virtually on top on you. If a train engineer sees you on a track, he or she will blow the whistle. Often it takes more than one blast to get the average person’s attention, say train engineers. But trains can’t stop the way motor vehicles can. A freight train has about 100 cars, weights 12 million pounds, and takes a full mile to stop. An optical illusion happens with tracks. When you see a train coming, it looks as if it is traveling half as fast, and is two times farther away from you than it really is. For example, if it is going 60 miles per hour and is half a mile away, it looks as if it is traveling 30 mph and is one mile away. (Operation Lifesaver)

Abraham Lincoln said...

You can fool some of the people all of the time, and all of the people some of the time, but you cannot fool all of the people all of the time.

Walter Scott

Oh! what a tangled web we weave When first we practise to deceive!

William S. Plumer

No wickedness on earth is more common than the various forms of deceit.

Expositor's Bible Commentary writes that...

Those who deceive others impair, in so doing, their sense of the distinction between truth and falsehood, and thus weaken their power of resistance to self-deceit and to imposition by others. (Gaebelein, F, Editor: Expositor's Bible Commentary 6-Volume New Testament. Zondervan Publishing)

Peter writes that prior to salvation we

were continually straying (planao - being led astray) like sheep, but now (we) have returned to the Shepherd and Guardian of (our) souls." (see note 1 Peter 2:25)

This miraculous transition from walking in darkness to walking in the light, should motivate every believer to conduct themselves in a manner worthy of the gospel (submit to and obey the government, do good deeds, don't malign, don't quarrel, be gentle and show meekness to all men, including the foolish, deceived, disobedient, etc!)

Clarke adds that

It is a true saying, “There are none so blind as those who will not see.” Such persons are proof against conviction, they will not be convinced either by God or man.

Although deceived in context describes who we once were (unbelievers), do not be deceived for believers can still fall prey to the wiles of deception! So beware! James writes

Do not be deceived (planao - present imperative + a negative =  literally stop being deceived - indicating that deception was already a fact), my beloved brethren. (James 1:16)

Paul warns the Galatians that when dealing with one caught in any trespass, they must be careful for

if anyone thinks he is something when he is nothing, he deceives (not planao but phrenapato) himself. (Gal 6:3).

James writes that

If anyone thinks himself to be religious, and yet does not bridle his tongue but deceives (not planao but apatao) his own heart, this man's religion is worthless. (Ja 1:26)

Clearly, the tragic truth is that the one who is deceived does not even know he or she is deceived! Given the "deceptive nature" of deception, it is not surprising that the writer of Hebrews exhorts us to

encourage one another day after day, as long as it is still called "Today," lest any one of you be hardened by the deceitfulness  (not planao but apate) of sin. (see note Hebrews 3:13)

Sin will deceive you. You are not getting away with that "little sin"...in fact your heart is being gradually hardened by it (and you don't even realize it!) Kill sin or it will kill you.

Paul goes on to warn the Corinthians of the danger of deception writing

Or do you not know that the unrighteous shall not inherit the kingdom of God (the spiritual sphere of salvation where God rules as King over all who belong to Him by faith)? Do not be deceived (planao - stop being deceived) neither fornicators, nor idolaters, nor adulterers, nor effeminate, nor homosexuals, nor thieves, nor the covetous, nor drunkards, nor revilers, nor swindlers, shall inherit the kingdom of God. (1Cor  6:9-10)

This list convicts us all...who among us does not covet from time to time? Occasional sins is not what Paul is referring to. Don't be deceived. If an individual habitually and as manner of their lifestyle commits these sins, Paul says they are not saved.

Ryrie agrees writing that

People whose lifestyles exhibit wickedness, not fruit, show they are unsaved and will, therefore, not inherit the kingdom of God. (The Ryrie Study Bible: New American Standard Translation: 1995. Moody Publishers)

In a similar warning to the Galatians Paul writes

Do not be deceived (present imperative + a negative =  literally stop being deceived) God is not mocked; for whatever a man sows, this he will also reap. For the one who sows to his own flesh shall from the flesh reap corruption, but the one who sows to the Spirit shall from the Spirit reap eternal life. (Gal 6:7-8)

Here are the 39 uses of planao in the NT...

Matthew 18:12 "What do you think? If any man has a hundred sheep, and one of them has gone astray (passive voice), does he not leave the ninety-nine on the mountains and go and search for the one that is straying? 18:13 "And if it turns out that he finds it, truly I say to you, he rejoices over it more than over the ninety-nine which have not gone astray.

Matthew 22:29  But Jesus answered and said to them, "You are mistaken (you err, you go astray) not understanding the Scriptures, or the power of God.

Matthew 24:4 And Jesus answered and said to them, "See to it that no one misleads you. 5 "For many will come in My name, saying, 'I am the Christ,' and will mislead many.