The Law of God is good, for by it God declares what men must do if they are to have perfect love in all things. Yet the Law of God is terrible for sinners, for in all that is says it condemns men to eternal death, for man, in his sin, cannot keep the law but can only be condemned by its righteous judgments.

In this, the Law is doing the work for which God created it. That is, even though men do not keep the Law the Law is still effective in men and accomplishes God’s purposes. This action of the Law upon the human heart has traditionally been divided into three aspects or uses: The Law threatens with death those who do not keep it and thus curbs much sin; the Law reveals sin where man is not even aware of it; and the Law instructs the Christian in those works that are pleasing to God. These three uses, or functions, are often summarized as the curb, the mirror, and the rule.

The third use of the Law, instruction in righteousness, has been controversial in the history of the Lutheran faith. Already in the generation following the Reformation some abused the liberty of the Gospel and taught that the Law had no use for the Christian at all and should not be taught to him. Against this error the Formula of Concord (Art. VI) responded that the Law was still necessary in the Christian life, for Christians still have a sinful and recalcitrant flesh that remains in rebellion against God at all times and cannot keep the Law (Rom. 7:21–23). Thus the Law still serves a godly purpose also in the elect (Rom. 7:13f.).

Yet the Law serves no purpose for righteousness. It neither does nor can assist the Christian in performing good works (Rom. 10:4). All it can do is reveal the sin that remains in His flesh that He might apply to Himself the judgments of the Law, and live a life of daily contrition and repentance. Thus, though we term the third use of the Law “instruction,” it is not instruction in the sense that it is teaching the Christian how to do good works but in the sense of discipline. By hearing the instruction of the Law the Christian daily reveals the sin in his flesh that He might strive against it and overcome it by the Gospel of the forgiveness of sins in Christ Jesus which is his through baptism (Rom. 6:1–11).

In this way the Law instructs us in the will of God, but when it instructs it simultaneously admonishes our old man of sin and delights our new man in Christ. But because we have both the old adam and the new man, we cannot always distinguish between godly and sinful desires. Therefore we need this instruction of the law. Wherever its instruction is heard our old man of sin is admonished, and in this we are convicted of sin and our new man rejoices and hears in the Law the goodness of God. But nevertheless, the Law does not grant the new man the ability or strength to keep the law, for the Gospel alone creates in the Christian the desire, strength, and ability to please God and to walk according to His commandments (Rom. 8:1–4).

In Christian preaching, one may choose the tone of his preaching (as for example in Luke 3:7–14 when John the Baptist instructs the tax collectors and soldiers gently, but the Pharisees he harshly condemns), but he cannot choose the use or aspect of the Law which will effect those who hear it. Rather it will function in whatever way God Himself has ordained (Isa. 55:11).

We reject the belief that after conversion the Law has no further use in the Christian life. We likewise reject the belief that the law is an instrument which is capable of reforming the life of the Christian and assisting him in performance of good works, except insofar as it reveals sin and the will of God.