“For when the Gentiles, which have not the Law, do by nature the things contained in the Law, these having not the Law, are a law unto themselves.”– This verse is not to be understood as affirming, as an historical fact, that any of the heathen ever did perfectly obey the law which they had, any more than the previous verse affirms that the Jews had. The main point in the argument is, that if men are justified by the law, their obedience must be entire and perfect; that this is not to be external only, or to consist only in hearing or in acknowledging the justice of the Law; and that the Gentiles had an opportunity of illustrating this principle as well as the Jews, since they also had a law among themselves.

“For when”–In verse 13 Paul stated a general principle: that only the doers of the Law can be justified; that is, if justification is attempted by the Law. In this verse and the next, he goes on to show that the same principle is applicable to the heathen.  Although they do  not have the written law of God, yet that they have sufficient knowledge of His will to take away every excuse for sin, and consequently that the course of reasoning by which he had     come to the conclusion that they were guilty is well founded.              

         WHEN:  (Grk.-hotan)–Literally:  “whenever.”  This does not go against the fact that God will do so by Jesus Christ“For the Father judgeth no man, but hath commended all judgment unto the Son(John 5:22). 

Paul is supposing a case which may occur; that is, he is presenting a “what if” scenario. This word “when”  (Grk.-hotan) does not imply that the thing shall certainly take place, but is one form of introducing a supposition, or of stating the connection of one thing with another (Matt. 5:11; 6:2,5,6; 10:19).  However, it is true that the main things contained in this, and the next verse, actually occurred, that the Gentiles did many things which the law of God required.

         “the Gentiles”
         Literally: “nations;”– In the original Greek there is no article, “the.”   This word
Gentiles means all who were not Jews.

Having refuted the perverse judgment of the Jews concerning the Gentiles, Paul now proceeds to show the just judgment of God against them. He now speaks directly of the Gentiles, in order to convince them.  Yet the concession he makes to these serves more strongly to convince the Jews. 

“which have not the Law”
Literally:  “not having law.”–Meaning those who do not have a
revelation, or the written Word of God.  Nor does it follow that the Gentiles, who have not had a Divine revelation, shall either perish because they did not have it; or their unrighteous conduct can go  unpunished because not having this revelation might be considered as an excuse for their
sins.  Having no revelation, such as the Jews had, they still had a law of nature (1:18. 32).

         WHICH:   (Grk.–hoItIn  es)–This is a double negative which shows class or kind. Translate as,“which are of a class, as to”, etc. 

“do by nature the things contained in the Law”
Literally:  “do the things of the Law.”  That is, without an outward rule; though this also,     strictly speaking, is by preventing grace.  Referring to the things which the law requires— the Ten Commandments being the substance of the law of nature. 

Paul has shown how the general principle “that God will render to every man according to his works (Prov. 24:12; Matt. 16:27; II Tim. 4:14) applies to the Jews; they will be judged by Law, and only law-doers will be justified.  He now shows that the same principle applies to the Gentiles. Although they do not a revealed and written law like the Jews, in any case, Gentiles, without it, should keep the things contained inthe moral principles of the Law of Moses.

“are a law unto themselves”
Literally: “themselves are a law.” It means that their own reason and conscience constituted a law, or prescribed that for them which the revealed Law did to the Jews.

         Their consciences and moral sense are a law.  They are not accountable to any other law, and are not to be judged by any dispensation different from that under which they live.  This is explained in the following verse.
         Paul is saying that even those who did not know the written law had an unwritten law within their hearts.  We would call it the instinctive knowledge of right and wrong.  Even the Stoics said that in the universe there were certain laws that operated which people broke at their peril–the
laws of health, the moral laws which govern life and living.  They (the Stoics) called these laws (Grk.–phusin), and urged men and women to live kata phusin, that is, “according to nature.

         It is Paul’s contention that in the very nature of human beings there is an instinctive knowledge of what they ought to do.  Even the Greeks would have agreed with that.  Aristotle said, “The cultivated and free-minded man will so behave as being a law to himself.”

VERSE 15:|
“Which show the work of the law written in their hearts, their conscience also bearing witness, and their thoughts the mean while accusing or else excusing one another.”

         “Which show”
         Literally:  “Who demonstrate.”  Who thus give evidence or show to themselves, to other men, and, in a sense, to God Himself

         “the work of the Law”–The substance, though not the letter, of it. 

The purpose, or object, which is anticipated or expected by the revealed Law; that is, to make known to man his duty, and to enforce his obligation to perform it.  But by no means does not mean that they had all the knowledge which the Law would impart, for then there would have been no need of a revelation.   However, as far as they had a knowledge of right and wrong, they coincided with the revealed will of God. In other words, the will of God, whether it had been made known by reason or revelation, will be the same so far as reason goes. The difference is, that revelation goes farther than reason.  It sheds light on new duties and doctrines.

“written in their hearts”– By the same One who wrote the commandments on the tables of stone. The revealed Law of God was written on tables of stone, and then recorded in the books of the O.T.

To a certain extent the law the Gentiles possesses,  the same requirements were written on their hearts. Though not revealed to them as to the Jews, yet they had obtained the knowledge of them by the light of nature.

         HEARTS:  (Grk.–kardias)–The word “hearts” here denotes the mind itself, as it does also frequently in the sacred Scriptures; not the heart, as the seat of the affections. It does not mean that they loved or even approved of the law, but that they had knowledge of   it; and that knowledge was deeply engraved on their minds.

“Their conscience”–Conscience may be either enlightened or unenlightened; and its use may be greatly perverted by false opinions. Its purpose is not to communicate any new truth; on the contrary, it is simply to express judgment, and to impart pleasure or inflict pain for a man's own good or evil conduct.  

         CONSCIENCE:  (Grk.–suneidēisis)-Literally: the judgment of the mind in respect to  right and wrong; or the judgment which the mind passes on the morality or immorality of its own actions, when it instantly approves or condemns them.  It has usually  been termed the moral sense, and is a very pirinciple in a moral government.

         The Greek word suneidesis means co-knowledge by the side of the original consciousness of the act. This second knowledge is personified as confronting the first. The Stoics used the word a great deal and Paul uses it twenty times  All men have this faculty of passing judgment on their actions. It can be over-scrupulous (I Cor. 10:25) or “seared” by abuse (I Tim 4:12), and it acts according to the light it has. Their thoughts one with another accusing or also excusing them.
          The purpose of conscience is to answer the purposes of an ever-presentt witness of a man's conduct; to compel him:
1.        To pronounce on his own doings, and therefore to excite him to virtuous deeds,
2.       To give comfort and peace when he does right, to deter from evil actions by making him, whether he will or no, his own executioner (see 9:1; John 8:9; Acts 23:1; 24:16; I Tim. 1:5).

By nature, every man approves or condemns his own acts; and there is not a profounder principle of the Divine administration than this compelling every man to pronounce on the moral character of his own conduct. Paul’s argument does not require him to say that conscience revealed any truth, or any knowledge of duty, to the Gentiles, but that its actual exercise proved that they had a knowledge of the law of God.  There is none of all its faculties which the soul has less in its power than this.

         “bearing witness”
         Literally:  “Witnessing with {them}.”  In a trial there are the
plaintiff, the defendant, and the witnesses. 

Conscience and sin itself are witnesses against the heathens. To bear witness is to furnish testimony or proof.  And the exercise of the conscience here showed or proved that they had a knowledge of the law. The expression does not mean that the exercise of their conscience bore witness of anything to them, but that its exercise may be alleged as a proof that they were not without some knowledge of the law.

“and their thoughts”
Literally:   “The thoughts.”– This supposes subsequent reflection, and it means that such reflections would only deepen and confirm the decisions of conscience.

         THOUGHTS:  (Grk.–logismos)–Literally:  “reasoning, thought, false argument or reasoning, opinions, sentiments.” Its meaning here may be expressed by our English word reflections. Their reflections on their own conduct would be attended with pain or pleasure. It differs from conscience inasmuch as the decisions of conscience are instantaneous, and without any process of reasoning.

         “accusing or else excusing”
         Literally: “Accusing or even excusing.” Accusingif their actions were evil
excusing—if their actions were good.

Paul does not say that a heathen's conscience always commends everything that he thinks, says, or does. In order for one to be set right with God by his own life he must always act in accord with his conscience and never have its disapproval. That, of course, is impossible, else Christ died for nothing (Gal. 2:21).  Jesus alone lived a sinless life.  For one to be saved without Christ he must also live a totally sinless life.

“one another”
Literally:  “Between one another; between themselves.” The expression sometimes means,  “in the meantime,” or “at the same time;” and sometimes afterward, or subsequently.

        ANOTHER:   (Grk.–allēlōn)–Some render this expression in connection with the Greek adverb (metaku), translated “in the mean while,” “between themselves.”

This view is also taken by many commentators, and this is its probable meaning.  If so, it denotes the fact that in their reflections, or their reasonings or discussions, they accused each other of crime, or acquitted one another; they showed that they had a law; that they acted on the supposition that they had. To show this was the purpose of Pau, and there was no further proof of it needed than that which he here has presented.
1.      They had a conscience, pronouncing on their own acts.
2.      Their reasonings, based on the supposition of some such common and acknowledged standard of accusing or acquitting, supposed the same thing.
Therefore, they condemned or acquitted themselves, if, in these reasoning and reflections, they proceeded on the principle that they had some rule of right and wrong, then the proposition Paul  was made out that it was right for God to judge them, and destroy them (2:8-12).

“In the day when God shall judge the secrets of men by Jesus Christ according to my Gospel”

“In the day”
Literally: “In a day.”  The definite article “the” is not in the Greek text.  This verse is  really connected with v. 12, since verses 13-15 are a parenthesis, and it implies that the heathen world, as well as the Jews, will be  arraigned at God’s Bar of Judgment.

Here the unfinished statement of verse 12 is resumed and continued. At that time God will judge all in righteousness, the Jew by the law which he had, and the Gentile by the law which he had. These principles of judgment shall prevail in that day when God shall judge the world.  Everything will then be shown to be what it really is. In that day will appear the law written in their hearts  as it often does in the present life.

“when God shall judge”        
Literally:   “When God judges.”  God is often represented as the
Judge of mankind (Deut.   32:36; Psa. 1:4; I Sam. 2:10; Eccl. 3:17; Rom. 3:6; Heb. 13:4).  This does not go against the   fact that God will do His judging by Jesus Christ.

“by Jesus Christ”
Literally:  “through Jesus Christ”–Paul now adds that this Judgment, which all are ready to admit, will be through Jesus Christ God has appointed His Son to administer judgment and it will not be directly by God the Father, but by Jesus Christ that it will be administered.  The fact that Jesus Christ is appointed to judge the world is many times taught in the N.T.: (Matt. 25:31-46; Acts 17:31, II Tim. 4:1; I Pet. 4:5, John 5:22, 27;  I Thess.4:16-18.

“For the Father judgeth no man, but hath commended all judgment unto the Son(John 5:22).  NEVER FORGET:  that Christ Jesus is God–“For in Him dwelleth all the fullness of the Godhead bodily” (Col. 2:9).

“according to my gospel”–And all this shall be farther exemplified and proved in the day when the secrets of men will be judged by Jesus Christ; which judgment shall be according to my Gospel—according to what I am now laying down before you, relative to the impartiality of God, and His righteous procedure in judging men.
1.        Not according to men’s opinions or prejudices,
2.        Not according to revelations which they never possessed, but,
3.        According to the various advantages or disadvantages of their political, religious, or domestic situation in life.

“the secrets of men”
Literally:   “The hidden things of men.”  Here specially referring to the unfathomed depths of
hypocrisy in the self-righteous whom Paul had to deal with. 

         On secret circumstances depends the real quality of actions, frequently unknown to the actors themselves (v. 29).  Men generally form their judgments, even of themselves, merely from what is apparent, or what they would like things to be  Their lives are often hidden from their fellow-men, but at the Judgment every secret shall be made brought out in the open.
         See Luke18:17; Eccl. 12:14, “For God shall bring every work into judgment, with every secret thing,” etc. (Matt. 10:26; I Cor. 4:5). This means the hidden desires, lusts, passions, and motives of men; the thoughts of the hearts, as well as the outward actions of the life. It will be a characteristic of the Day of Judgment that all these will be brought out, and receive their appropriate reward. The propriety of this is apparent, for
1.      It is by these that the character is really determined. The motives and principles of a man constitute his character, and to judge him impartially these must be known.
2.      They are not judged or rewarded in this life. The external conduct only can be seen by men, and of course that only can be rewarded or punished here.
3.      Men of pure motives and pure hearts here are often persecuted, maligned, and often overwhelmed with disgrace and other forms of dishonor. 

Therefore, it is proper that the secret motives of their conduct should be brought out, and approved.  On the other hand, men of base motives–men of unprincipled character, and who are corrupt at the heart–are often lauded, flattered, and exalted into public estimation. So it is proper that their secret principles should be detected, and that they should take their proper place in the government of God. In regard to this expression, we may further remark:

a.       That the fact, that all secret thoughts and purposes will be brought into judgment, endows the judgment with an awful character.

Who should not tremble at the idea that the secret plans and desires of his soul, which he has so long and so studiously concealed, should be brought out into noon-day in the judgment?  All his artifices of concealment shall be then at an end. He will be able to practice disguise no longer. He will be seen as he is; and he will receive the doom he deserves. There will be one place, at least, where the sinner shall be treated as he ought. 

b.      To execute this judgment implies the power of searching the heart, of knowing the thoughts, and of developing and unfolding all the purposes and plans of the soul. Yet this is entrusted to Jesus Christ, and the fact that He will exercise this shows that He is Divine.

“according to my Gospel”–According to the gospel which I preach (comp. Acts 17:31; II Tim. 4:8); according to my teaching as a  preacher of the Gospel; according to what Paul preaches (I Cor. 15:1) and which is the true gospel. 

         This does not mean that the gospel which Paul preached would be the rule by which God would judge all mankind, for he had just said that the heathen world would be judged by a different rule (v. 12).  But it does mean that he was entrusted with the gospel to make it known; and that one of the great and prime articles of that gospel was, that God would judge the world by Jesus Christ.  To make this known he was appointed; and it could be called his gospel only as being a part of the important message with which he was entrusted.
         People have the false idea that because they might happen to be good people, that is, they think they are, that they will be saved.  But God is going to judge the do-gooders.   And He will judge them by Jesus Christ who said that if a man even looked upon a woman to lust after her, he is guilty of adultery (Matt. 5:27-28).  This is only one example of the secrets of the human heart.
         The Lord Jesus Christ will be the Judge (John 5:22); and it will be according to the gospel which Paul preached. The Gospel will either save or condemn men. By the words of Christ shall men be judged.  If a man refuses the gospel, he is damned; if he receives the Gospel and it’s message, he will be saved from being damned.   It is just that simple.