What does "by the law is the knowledge of sin" mean (Romans 3:20)?

It is, therefore, a manifest impossibility that any one can get life and righteousness by that which can only curse him; and unless the condition of the sinner, and the character of the law are totally changed, it can do nought else but curse him. It makes no allowance for infirmities, and knows nothing of sincere, though imperfect, obedience. Were it to do so, it would not be what it is, "holy, just, and good." It is just because the law is what it is, that the sinner cannot get life by it. If he could get life by it, it would not be perfect, or else he would not be a sinner. It is impossible that a sinner can get life by a perfect law, for inasmuch as it is perfect, it must needs condemn him. Its absolute perfectness makes manifest and seals man's absolute ruin and condemnation. "Therefore by deeds of law shall no flesh living be justified in his sight; for by the law is the knowledge of sin." (Rom. 3:20) He does not say, "by the law is sin," but only "the knowledge of sin. "For until the law, sin was in the world; but sin is not imputed when there is no law." (Rom. 5:13) Sin was there, and it only needed law to develop it in the form of "transgression." It is as if I say to my child, "you must not touch that knife." My very prohibition reveals the tendency in his heart to do his own will. It does not create the tendency, but only reveals it.

But this is not all. The law has its use, namely, in bringing out the consciousness of what we are - of our state. Was it the fault of the law, this dominion of sin, while we were under it? Nay, it was the fault of the sin, and lust which the law condemned. "But that," says the apostle, "I had not known, unless the law had said, Thou shalt not lust." If he had murdered, he would have known the fact; his natural conscience would have taken cognisance of it. But we are not treating of sins now (as before observed), but of sin. I had not known that, unless the law had dealt with its first movements as evil. Many have committed no crimes - have neither murdered, stolen, nor committed adultery; but who has never lusted? It would be to say, I am not a child of Adam at all. And note here, we are not speaking of guilt by acts, but of state; not of judgment, nor of forgiveness, but of deliverance, of setting free. And note further here, how great the error is of those who hold lust not to be sin if not consented to. The object here is to detect the evil nature by its first motion - lust. Not, indeed, what we have done, but what we are; and the sinfulness of flesh is detected by that first movement, which is lust - will in evil. It proves, by its sinfulness, the sinful source in me. I know that in me dwells no good. Important though humbling discovery! Not, I repeat, what I have done, but what I am; but how important that! What simple folly the thought to make the child of Adam good, unless he be born again!

(V. 20) Moreover the law, that brings all under judgment to God, holds out no possibility of man removing the judgment by any efforts of his own. "By the deeds of the law shall no flesh be justified in His sight". The law, indeed, convicts of sin, "for by the law is the knowledge of sin", but it cannot remove the sins, or deliver from the power of sin. The law is but a plumb-line to show the crookedness of the wall. It would be as foolish to think that a crooked wall could be made straight by holding a plumb-line against it, as to think that a guilty sinner could be justified by the law. Thus the law convicts us of, not only being sinners before God, but also of being helpless sinners. Our ruin is total, and irretrievable, as far as we are concerned. Man is not only a fallen creature driven out from Paradise, he cannot find his way back. The law which was given for life, if a man kept it, has become a ministration of death and condemnation.

I am more deeply convinced than ever, by renewed study of Romans and other scriptures, that the view I have insisted on, as to a new nature and place in resurrection, as contrasted with flesh under law, is not only true, but is the great fundamental point on which the Apostle Paul insists as distinguishing Christianity. That, while surely sins are expiated and put away, "all are under sin" is what he is dwelling upon, and that wholly as in flesh, and hence death and a new state come in, through grace, in Christ. Besides the blessed fact of putting away sins, this is the truth of the Romans - righteousness being established by the obedience of Christ as such. But this, too, in contrast with law. Even as to convincing power, he does not say by the law is the knowledge "of sins," for conscience told that, but the knowledge "of sin." "All have sinned," is in the end of Romans 3; so in verses 12-16 is offences under law specially. Both "sins" and "sin" in chapter 4:7-8; so verse 25. In chapter 2:12, is actual sinning, as in chapter 3:23. From chapter 6, where death is applied, "sin" is the subject.

Thus all stand inexcusable in their guilt before God; and this, because law-works cannot justify — still less of course the works that man's mind suggests, or that the will of others may extort. If any works could justify anybody, those of God's law must be the surest benefit to the Jew. But the truth is that no flesh shall be justified from any such source in His sight; for contrariwise law never produces holiness but is only the means of arriving at a full knowledge of sin.

"What then shall we say? [Is] the law sin? Let it not be. But I should not have known sin unless by law; for lust also I had not known unless the law had said, Thou shalt not lust. But sin, having taken occasion by the commandment, wrought out in me every [manner of] lust; for apart from law sin [is] dead. But I was alive apart from law once; but the commandment having come, sin revived, and I died; and the commandment that [was] unto life was even found for me unto death. For sin, having taken occasion by the commandment, deceived, and by it slew me. So that the law [is] holy, and the commandment holy, just, and good. Did then the good become death to me? Let it not be; but sin, that it might appear sin, working out death to me by the good, that sin might become excessively sinful by the commandment." (Ver. 7-13.)

Thus the apostle takes pains to relieve the law of all censure. Far from this, it was the excellency of the law which was so fatal to the sinner. It knows no mercy; it cannot mitigate its terms or its punishment. By the law is the full knowledge of sin, said the apostle in Romans 3. So here, whether objectively or in inward consciousness, law is the means of its discovery, not from any defect in law but from the sinfulness of sin, which is here personified as the foe that is seizing a point for attacking man. But here the apostle is occupied with the proof not of guilty acts but of an alien rebellious nature, and hence singles out the last commandment, the prohibition of covetousness or lust, as the most adapted to convict of sin, not merely of sins. And how true this is! Who does not know the irritation produced by a restraint on the will? So all manner of lust is excited, for apart from law sin is dead: let the commandment have come, and all is over. It never did, it cannot, improve the flesh, but contrariwise provokes it by the curb applied. What is really wanted is a new nature and a transforming object; but law neither communicates the one nor reveals the other: grace does both through Christ our Lord. The fault is solely in the first man, the deliverance is exclusively in the Second. Law sets forth what man ought to be, but condemns him necessarily for the sin it makes active and manifest, without the smallest power to save from it any more than to strengthen against it. On the contrary, says the apostle, "I was alive apart from law once, but, the commandment having come, sin revived and I died." Thus what pointed to life only proved an instrument of death. But if the living man die, law cannot quicken the dead. It is the Son's to quicken whom He will, even as the Father does. But here again the apostle is careful to lay all blame on sin, which, having taken occasion by the commandment, slew by it the deceived man. Thus the law is vindicated, the nature it in vain appeals to is alone in fault; for the commandment is holy, just, and good. Did then the good become death to me? asks the apostle. Not so; it is sin here again he treats as the true culprit, "sin that it might appear sin, working out death to me by the good, that sin might become excessively sinful by the commandment." Could the Jew, however prejudiced against grace, however prepossessed in favour of law, complain with justice? Is it not the evident truth?

"Is the law sin?" is the next question raised. It springs logically from the statement that the passions of sins, coming out of an evil, sinful heart, were by the law and bringing forth fruit unto death. Still another "God forbid" is the answer. The law was given that we might have through that law the knowledge of sin. "I had not known sin, but by the law." I would not be conscious of lust, unless the law said, "Thou shalt not covet." The law given by a holy God is God's detective. The law forbids and the commandment at once brings out what is in the heart of man. Therefore, no blame can be put upon the law. Sin is that which must be blamed. Sin is lawlessness, rebellion against God and the law brings out that rebellion. Therefore apart from the law sin was dead, that is, dormant. But as soon as the commandment is given, the evil heart rebels against it and man is detected to be a sinner and a transgressor. Let us notice the change of the pronoun "we" to "I." Some thirty times this little word "I" is found in verses 7-25. We are brought upon the ground of personal experience; it has to be discovered and learned experimentally. The Apostle personifies this experience and speaks thus personally describing how a believer learns the lessons about the law, how the law cannot help a justified believer, and but makes of him a wretched man. It must also have been his own experience.

"For I was alive without the law once, but when the commandment came, sin revived, and I died." This is the experience of a man who is ignorant of the spirituality of the law. He thinks himself alive, but when the commandment came, its spiritual demands realized (the law is spiritual, verse 14), the false notion of being alive was detected, for sin revived and he died, which means that sin, discovered by the law, condemned him to death. "And the commandment which was unto life was found for me to be unto death." In connection with the commandment, the law, it is written, "This do, and thou shalt live." And so in this experience--he tries next to get life by the law, but he found it was unto death, for the declaration of the law is "Cursed is every one that continueth not in all things which are written in the book of the law to do them" (Galatians 3:10; Deuteronomy 27:26). He speaks of sin, his evil nature, as one who had deceived him into all this, so that the law could manifest its power in slaying him. Verse 12 is the real answer to the question, "Is the law sin?" The law is holy, and the commandment holy, and just and good. And because the law is holy it gives knowledge of sin and detects sin, bringing it to light in all its hideousness and then pronounces the sentence of death. One other question is asked, "Was then that which is good (the law) made death unto me?" God forbid. But sin, that it might appear sin, working death in me by that which is good; that sin by the commandment might become exceedingly sinful." It all comes back upon sin (the evil nature, the flesh). Thus by the commandment sin becomes exceeding sinful.

Are now described: “Without the law sin was dead — I was alive without the law once.” Immediately, however, he applied the law to his own case, took its medicine, as it were, his eyes were opened, and he became sensible to his condition; “But when the commandment came sin revived and I died.” It stirred up the evil of his heart. Not that it made his heart worse, but it made him feel his badness. The law said, “Thou shalt not covet;” thou shalt not have an acquiring or a grasping desire; and no sooner did the commandment go forth not to wish for a special thing, than it roused up the bad nature to long for that which was forbidden. Like a child who, when told not to look into the basket, immediately desires to do it, so poor, weak, and sinful human nature, when told by the law of God not to covet, immediately falls a longing. It is not that the commandment makes the child naughty, but the fact of the prohibition proves what the child is. The motions of sin are thus rendered active by the law. Sin exists; the nature is there; but the desires of sin are brought into action by the law bidding them be silent. And this sense of what self is, wrings from the broken heart of the believer the cry, “Oh, wretched man that I am! who shall deliver me?”

The chief use of the law is to prove that, we have in us an evil principle called "sin". The Apostle says, "I had not known sin, but by the law". He does not say 'sins', but 'sin'. He would have been conscious of sins had he never known the law. We need no law to tell us it is wrong to steal and murder. Natural conscience will convict a men of wrong conduct. But conscience would never reveal to a man his inward state of sin. The law said, "Thou shalt not lust". This one command applies to the inward man, and, not as with the other nine commands, to the outward conduct. The outward conduct might be blameless, and consequently the conscience easy having no sense of judgment or death. But seeing there is sin in us, the immediate effect of the law saying "Thou shalt not lust" is to stir up lust, and at once the conscience knows that the law is broken and realises that death is the result. "Sin revived, and I died". The law that was ordained to life if obeyed, brings death upon the conscience when broken.

The truth is, as the apostle teaches us, "the law entered that the offence might abound." (Rom. 5:20) This shows us, very distinctly, the real object of the law. It came in by the way in order to set forth the exceeding sinfulness of sin. (1 Cor. 7:13) It was, in a certain sense, like a perfect mirror let down from heaven to reveal to man his moral derangement. If I present myself, with deranged hair, before a mirror, it shows me the derangement, but does not set it right. If I measure a crooked wall, with a perfect plumb-line, it reveals the crookedness, but does not remove it. If I take out a lamp on a dark night, it reveals to me all the hindrances and disagreeables in the way, but it does not remove them. Moreover, the mirror, the plumb-line, and the lamp, do not create the evils which they severally point out; they neither create nor remove, but simply reveal. Thus is it with the law; it does not create the evil in man's heart, neither does it remove it; but, with unerring accuracy, it reveals it.