"For" (gar is a marker of cause or reason positioned after a preceding clause and introducing the reason or cause for what has just been stated) looks at the last clause of Romans 2:12 and explains why the Jews shall be judged by the Law.

Mere knowledge of the Law ("hearers") will not satisfy divine justice for it is not the hearers, but the doers, that are justified (cf Ja 1:22). God’s righteous judgment is not withheld because someone has heard the Law; it is only held back if someone has "done" the Law.

The Jew may think that he is saved because he has the Law; but Paul is saying that the question he needs to address "Have I kept the Law?" The Jews may have possessed the Law but they did not practice the Law. And of course no man can "practice the law" unless they are given a divine "heart transplant" which is exactly what Paul is building up to in his indictment of everyone still in Adam and dead in their trespasses and sins. In a similar manner, a Gentile might suppose that he is saved because he has kept the dictates of his own conscience. Paul is arguing logically that clearly this is not possible.

Both groups

"...will be condemned, not because they have the Law or do not have the Law, but because they have sinned." (Morris)

NOT THE HEARERS OF THE LAW ARE JUST BEFORE GOD: ou gar hoi akroatai nomou dikaioi para (to) theo:  (Ezek 33:30-32; see notes on Matthew 7:24-25; Matthew 7:26-27; Matthew 7:13-14; Matthew 7:15-16; Matthew 7:17-20; Matthew 7:21 Matthew 7:22-23; Lu6:49; 8:11-15;  Js 1:19,22-25)

Hearers (202) (akroates from the verb akouo = hear with attention) describes those who of those who sat passively in an audience and listened to a singer or speaker.

Vincent writes that "hearers" are those...

Like the Jews...heard it regularly in the synagogues. (Akroates is found) Only here in Paul. Three times in James. It brings out, better than the participle hoi akouontes those that hear, the characteristic feature; those whose business is hearing.

Jews attended their synagogues, week after week hearing the law read and explained to them. They were professional hearers but should have been proficient doers! (cf Ja 1:22)

MacArthur adds this helpful note

"Paul here does not use the usual Greek term for hearing (akouo) but the word akroates, which was used of those whose business it is to listen. The idea is much like that of a college student. His primary purpose in class is to listen to the teacher’s instruction. Normally, he also has the responsibility of being accountable for what he hears and is tested on it. If he is simply auditing, however, he is required only to attend the class sessions. He takes no tests and receives no grade. In other words, he listens without being held accountable for what he hears. In many synagogues during Paul’s time, teaching did not focus on Scripture but on the system of man-made traditions that the rabbis had developed over the centuries since the Exile. Frequently, God’s Word in the OT was merely read and listened to, without explanation or application. Most Jews, therefore, were simply “auditing the course,” hearers of the Law and nothing more. But God recognizes no mere “auditors” of His Word. The more a person hears His truth, the more he is responsible for believing and obeying it. Unless there is obedience, the greater the hearing, the greater the judgment."

Just (dikaios) is an adjective which describes the man who is in accordance with what God requires. God is totally righteous because He is totally as He should be. The righteousness of God which He requires is all that God is, all that He commands, all that He demands, all that He approves and ultimately all that He provides (through Christ).

Note that "not" is the Greek word "ou" which signifies absolute negation of what follows. Paul is saying that merely "hearing" the Law justifies absolutely no one. The Jew boasted in knowing the Law, but Christ said, "None of you keep the Law." Applying this passage to the modern church, in the opinion of many evangelical pastors there are many individuals who upon hearing the gospel preached have made an outward "profession" but whose lives fail to exhibit fruit in keeping with genuine repentance (Mt 3:8) or good works (Eph 2:10) that indicate that they have been truly born again.

BUT THE DOERS OF THE LAW WILL BE JUSTIFIED: all hoi poietai nomou dikaiothesontai (3PFPI): (Ro 3:20,23; 10:5; Luke 10:25-29; Galatians 3:11,12) (Doers Mt7:21; 12:50; Lu11:28; 2Co8:11; Ja1:22-27; 4:11) (justified 3:30; 4:2-5; Ps 143:2; Luke 18:14; Acts 13:39; Galatians 2:16; 5:4; James 2:21-25) (See Torrey's Topic Justification before God, see articles in ISBE Easton)

"Justified" is dikaioo  (Click for all 14 uses of dikaioo in Romans) which is defined as

"the act or process by which a man is brought into a right state as related to God”. (Vincent)

The Law demands perfect and continuous obedience for one to be "justified". Paul has clearly stated that no one is accounted righteous simply because he hears or knows what the Law says. The only conceivable way of being justified under the Law would be to keep it in its entirety. But since all men are sinners, it is impossible for them to do this. So this verse is really setting forth an ideal condition rather than stating something that is capable of human attainment.

Constable comments that...

It is not hearing the law that makes a person acceptable to God, but doing what it commands (Ro 2:13). “Justified” is a legal term that is suitable in this discussion of law observance. Justification is a legal verdict. It reflects a person’s position under the law. The justified person is one whom God sees as righteous in relation to His law (cf. Deut. 25:1). The justified person is not necessarily blameless; he may have done things that are wrong. Nevertheless in the eyes of the law he is not culpable. He does not have to pay for his crimes. Paul said in Ro 2:13 that God would declare righteous the person who did not just listen to the Mosaic Law but did what it required. The Law warned that anything short of perfect obedience to it, even reading or studying it or hearing it preached and taught, which Jews relied on, made a person guilty before God (Deut. 27:26; cf. Gal. 3:10). Moses therefore urged the Israelites to accept and believe in the promised Messiah (e.g., Deut 18:15). (Constable's Expository Notes on the Bible) (Bolding added)

Paul will bring the truth about justification to fruition in Romans 3. In this chapter he is making it clear that no man in his own strength could be justified.

MacDonald has a nice summary of this section

"The NT teaches emphatically that it is impossible for man to be justified by law-keeping (Acts 13:39; Ro 3:20; Gal 2:16, 21; 3:11). It was never God’s intention that anyone be saved by the law. Even if a person could keep it perfectly from this day forward, he still would not be justified, because God requires that which is past. So when verse 13 says that doers of the law will be justified, we must understand it as meaning that the law demands obedience, and if anyone could produce perfect obedience from the day he was born, he would be justified. But the cold, hard fact is that no one can produce this." (MacDonald, W., & Farstad, A. Believer's Bible Commentary : Old and New Testaments. Nashville: Thomas Nelson)

William Newell writes

"Yet it is deeply instructive here to quote a passage like that of [Lu 1:6], concerning Zacharias and Elizabeth: "They were both righteous in the sight of God, walking blamelessly in all the commandments and requirements of the Lord." Now their walk was not the ground of their acceptance (Ed note: but is was the fruit of their faith), although only such as they are accepted! For they were subject to God’s Word, not mere hearers, but doers. (Ed note: again the only way Zacharias & Elizabeth could have been righteous "doers" is because they had at some point in time believed God's promises concerning the Messiah and God had reckoned their faith to them as righteousness [cf Ro 4:5] Luke does not tell us when they believed but from Romans & Galatians there is no other way they could have been declared righteous). The first verse of the book of Job (Job 1:1) describes another such person. Indeed, at heart all God’s saints are such."  (Romans 2)

"For" (gar is a marker of cause or reason positioned after a preceding clause and introducing the reason or cause for what has just been stated) and here looks back not to v13 but to v12. Paul is explaining that the Gentiles also have a law so to speak by which they will be judged. Paul explains in this section that the Gentiles can be condemned without the law because their conscience (which is the work of the law written in their hearts) is enough to condemn them. As testimony to the truth of this principle, it is interesting to note that many of the unsaved pagan writers of  Paul’s day referred to the "unwritten law" within man. Even these pagans recognized that there was something instinctively present within a man or a woman which tries to direct us in the right way. Remember that although all men are totally depraved in the sense that they cannot do anything that is righteously good, they can do a "man kind of good" like honoring their parents, paying their debts, etc. But every time they do that they prove that there is a law within them that points to that as good. Are they lost? Yes. Can they claim ignorance? No. As Paul pointed out in Romans 1, creation is around them proclaiming that God exists. In Romans 2 Paul is piling up the evidence against them, showing that by their conduct they prove that they have an inner moral law.

Stedman writes:

"Now, men are continually charging God with injustice because, they say, He condemns men to hell who have never heard of Jesus Christ. This is the most frequently voiced charge against the Christian gospel. We are always hearing somebody say, "Well, what about the heathen who never hear about Christ? How can a just God condemn them to hell without their hearing about Christ?" But, you see, God never condemns anybody on that basis. As we are told right here...That is, if you disobey the truth that you have, even though you have never heard of Moses or of Christ, you perish, not because you didn't hear of Moses or of Christ, but because you have disobeyed truth that you already know -- that is the whole point. If you know of Moses and of Christ, and you still disobey the truth, you perish also, because your condemnation is even greater -- because of the greater light involved. (Ed note: See above for discussion of the principle of judgment proportionate to light received) But, as it says here, even pagans have a form of basic law written on their hearts, and this is the basis of God's just condemnation of man. It is because they are not what they themselves know they ought to be. In other words, God judges you, not by some artificial standard of His, but by your own standard."

Stedman goes on to give an illustration of Paul's point:

"Recently, I was down in Newport Beach, teaching a Bible Class in a home. Quite a number of non-Christians were there, and one of them was a man from just across the street. He was a very charming individual, but he had made it known in the neighborhood already that he had no use for Christianity. As he came in the door, the first thing he said was, "I have come to be the Devil's advocate. I think the Devil needs a representative here tonight." We welcomed him, and told him to curl his tail around a chair, and sit down. As I began to speak on the opening chapter of Genesis, dealing with God's word to man, I could see in his face that this man had let down his guard. I don't think he was aware of how much he was revealing, but in that man's eyes I saw hunger written like I had never seen it before. At the question time, he, of course, came up with the usual question : "How about those that God condemns who never hear about Christ?" I answered (to all in the room), "Let me ask you this: Which of you has lived up to your own ideals? -- because God won't judge you on the basis of something that you have never heard, but on the basis of what you already know. Now tell me: Who of you has lived up to his own ideals? Which of you has never deliberately done wrong? Which of you can say that you measure up to your own standard of what you ought to be?" You could just hear the silence in that room! You see, it is not by some artificial standard that we stand condemned before God; it is because of what we know in our hearts about ourselves. This indicates that God measures us by our own yardstick." (Romans 2:1-16 The Secrets of Men)

GENTILES WHO DO NOT HAVE THE LAW DO INSTINCTIVELY THE THINGS OF THE LAW: ethne ta me nomon echonta (PAPNPN) phusei ta tou nomou poiosin (3SPAS): (12; 3:1,2; Deuteronomy 4:7; Psalms 147:19,20; Acts 14:16; 17:30; Ephesians 2:12) (do 27; 1:19,20; 1 Corinthians 11:14; Philippians 4:8) (See Greek/Gentile in Easton, Smith, ISBE, Torrey's Topical)

Without knowing the written law of God, men and women in pagan societies by nature, instinctively value and attempt to practice justice, honesty, compassion, goodness toward others, etc, this practice testifying to the fact that the divine law has been written in the heart of even the most primitive tribesman. While Paul says that a Gentile may by nature do the things contained in the law, he is very careful not to say that a Gentile could fulfill the requirements of the law by nature.

THESE, NOT HAVING THE LAW, ARE A LAW TO THEMSELVES: houtoi nomon me echontes (PAPMPN) heautois eisin (3PPAI) nomos:

"The Gentiles do not have the Law; but whenever they do by instinct what the Law commands, they are their own law, even though they do not have the Law" (TEV),

"Even when Gentiles, who do not have God's written law, instinctively follow what the law says, they show that in their hearts they know right from wrong." (NLT)

"For example, whenever non-Jews who don't have laws from God do by nature the things that Moses' Teachings contain, they are a law to themselves even though they don't have any laws from God." (GWT)

The Gentile's practice of some good deeds and their aversion to some evil ones demonstrate an innate knowledge of God’s law and this knowledge will actually witness against them on the day of judgment.

John Calvin adds that here Paul

"...shows that ignorance is in vain pretended as an excuse by the Gentiles, since they prove by their own deeds that they have some rule of righteousness."

To reiterate, Paul is simply saying that God has written on the heart of every man a basic moral code. That code is similar to the things contained in the Ten Commandments. This universal moral code consists of things like "Do not steal," "Do not cheat," "Tell the truth," "Honor your parents," "Keep your word," "Help the poor," "Do not kill," etc. It would be hard to find a culture anywhere in the world where those moral values are not honored.  The Greek poet Sophocles spoke of "the unwritten and indelible laws of the gods." The Platonic philosopher Plutarch called it "a law which is not written in books, but implanted in the heart of man." In fact, this concept of a universal moral code was widely discussed by the Greeks and Romans. Paul simply picks up that concept and applies it to the Gentiles.

Don't misunderstand what Paul is saying with the phrase "a law to themselves". He is not implying that these "obedient Gentiles" made up their own law (as we often use the expression in modern parlance describing a rebel as a "law unto himself"), but that they were obedient to conscience, the work of the law residing in themselves.

Note also that while Paul that a Gentile, may, by nature do the things contained in the law; he does not say that a Gentile could fulfill the requirements of the law by nature.

One other thought to keep in mind when reading Paul is that the word “Law” can be confusing, and can refer to the Pentateuch, to the entire Old Testament, to the Ten Commandments, to the whole body of God’s requirements for Israel, and to the way of life adopted by the covenant community. In Ro2-3 the basic meaning of “law” is “God’s revealed requirements for righteous living.”

Dirty Hands (Our Daily Bread, Copyright RBC Ministries, Grand Rapids, MI. Reprinted by permission. All rights reserved)

One of William Shakespeare’s most intriguing characters is Lady Macbeth. Having heard a prophecy that her husband would become king, she convinced him to assassinate the reigning monarch. When the bloody deed was done, Macbeth was conscience-stricken. His wife rebuked his squeamishness and helped him cover up the crime. Her husband was crowned king. But that wasn’t the end.

Lady Macbeth’s initial resolve turned to remorse. She grew mentally unstable, and couldn’t stop washing her hands. “Will these hands ne’er be clean?” she asked. Finally, the guilt drove Lady Macbeth to suicide.

Guilt is an emotion that can weigh us down whenever we cross a moral boundary. All of us are capable of feeling guilty when we violate the law of God written in our hearts (Romans 2:14-15). If we continue to sin willfully, however, we will dull our conscience.

Lady Macbeth is a good reminder of a biblical principle: Whatever we sow, we will certainly reap (Galatians 6:7-8). When we feel temptation, we need to listen to our conscience—not try to silence it. It’s far better to avoid committing an act we will later regret than to live with the consequences. —Dennis Fisher

Sometimes there’s just one step to go
Before we yield to sin,
But God will help us to say no
If we trust His power within. —Hess

Show (1731) (endeiknumi from en = in, to + deíknumi = show)

Showing (1731) (endeíknumi [word study] from en = in, to + deíknumi = explain meaning or significance of something by demonstration) means to indicate by word or act.  The idea is to show forth, demonstrate, prove, whether by arguments or acts.

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. It represents the inner person, the seat of motives and attitudes, the center of personality. In Scripture kardia is much more than emotion or feelings, but includes the thinking process and particularly the will.

Barclay commenting on the "Work of the Law" writes that...

We would call it the instinctive knowledge of right and wrong. The Stoics said that in the universe there were certain laws operative which a man broke at his peril—the laws of health, the moral laws which govern life and living. The Stoics called these laws phusis, which means nature, and urged men to live kata phusin, according to nature. It is Paul’s argument that in the very nature of man there is an instinctive knowledge of what he ought to do. The Greeks would have agreed with that. (Barclay, W: The Daily Study Bible Series, Rev. ed. Philadelphia: The Westminster Press)

People who have never heard God's word directly still have a moral compass that they are accountable to. E.g., all men know it is wrong to lie, steal, and murder.  Mankind recognizes that there is a code of ethics. In fact man has a guilty conscience because he violates that very code of ethics within him.

William Newell  (Romans 2) asked Chinese who had never heard the Law or the gospel if they knew these things were wrong; they all admitted they did. Even those persons who have never heard of the Bible have still been preached to with sufficient clarity (God has made it evident within them - see note Romans 1:19, as well as without - see note Romans 1:20) to remove every excuse from their hearts forever. He is not- saying that the Law of Moses is written on their hearts, as people often say, but that the work of the law, i.e., what the law requires of people, is written there.

MacArthur makes an interesting observation noting that...

The fact that such people did good things, knowing they were ethically good, proves they had knowledge of God’s Law written in their hearts. Therefore if those people never come to trust in the true God, their good deeds will actually witness against them on the day of judgment. (MacArthur, J: Romans 1-8. Moody)

Unregenerate people do relative human good, but they don't do good in terms of spiritual righteousness. Their good is not based on the right motive because nothing is truly good unless it is done for the glory of God. But they do good in a relative human sense. When they do that they show the law of God at work in them. They do good in the right manner if not for the right motive. (Romans 2-11-16 Principles of God's Judgment)

Thus Paul explains why the Gentile can be condemned without the