“The question might here be raised why it is that the Law leads men into the horrible sin of despair. That is merely an accidental feature of its operation. In and by itself the Law, too, is good.
Let me follow this up with a passage from Luther’s Commentary on Galatians. On Gal. 2, 3. 4 Luther says: “Accordingly, when your conscience is terrified by the Law, and you are wrestling with God, the Judge, do not consult your reason or the Law, but take your stand alone on the grace of God and His word of consolation. Cling to this and act as if you had never heard a word of the Law. Enter into that darkness (Ex. 20, 21) where neither the Law nor human reason gives its light, but only the dark word of faith. The believer relies with a certainty on being saved in Christ, without the Law and regardless of it. Thus the gospel, without, and regardless of, the light of the Law and reason, leads us into the darkness of faith, where the Law and reason exercise no authority. We must, indeed, hear the Law also, yet in its proper place and at the proper time. When he has come down from the mountain, he is a legislator and governs the people with the Law. In this manner our conscience is to be exempt from the Law, but ours is to obey the Law. … Hence, any person who understands well how to distinguish the Gospel from the Law may thank God and know that he is a theologian. In times of tribulation, indeed, I do not know how to do this as efficiently as I should. Both teachings are to be distinguished in such a manner that you place the Gospel in heaven, the Law on earth; that you call the righteousness which the Gospel proclaims a heavenly and divine righteousness, the righteousness which the Law proclaims an earthly and human righteousness; and that you are as careful to distinguish the righteousness of the Gospel from the righteousness of the Law as God with great care has separated heaven from earth, light from darkness, day from night. One of these doctrines shall be the light of day, the other the darkness of night. Would to God that we could put them still farther apart!
“Therefore, when we are speaking of faith and are ministering to men’s consciences, the Law is to be utterly excluded; it must remain on earth. When you treat of what men are to do, light the night-lamp of works, or of the righteousness that is by way of the Law. Thus the sun and the unmeasured light of the Gospel and of grace is to shine during the day; the lamp of the Law, however, at night. A conscience, then, that has been thrown into terror by feeling its sin should argue thus: I am now engaged in earthly tasks. Here let the donkey labor, slave, and carry the burden that is laid upon him. That is to say, Let the body with its members be subject to the Law, But when you ascend to heaven, leave the donkey with its burden on earth. For the conscience of a believer in Christ has nothing to do with the Law and its works and the righteousness of this earth. Thus the donkey stays in the valley, while the conscience, with Isaac, goes up into the mountain, ignores the Law and its works, and keeps its eye only on the forgiveness of sin, on nothing but that righteousness which is exhibited and given to us in Christ. … This point of doctrine, vis., the distinction between the Law and the Gospel, we must needs know because it contains the sum of all Christian teaching. Let every one who is zealous to be godly strive, then, with the greatest care to learn how to make this distinction, that is, in his heart and conscience. The distinction is made easily enough in words. But in affliction you will realize that the Gospel is a rare guest in men’s consciences, while the Law is their daily and familiar companion For human reason has by nature the knowledge of the Law. Therefore, when the conscience is terrified by sin, which the Law points out and magnifies, you are to speak thus: There is a time to die, and there is a time to live; there is a time for acting as if you were ignorant of the Gospel. At this moment let the Law begone, and let the Gospel come; for now is not the time to hear the Law, but the Gospel. But how about this? You have not done any good; on the contrary, you have committed grievous sins. I admit that, but I have the forgiveness of sins through Christ, for whose sake all my sins have been remitted. However, while the conscience is not engaged in this conflict, while you are obliged to discharge the ordinary functions of your office, at a time when you must act as a minister of the Word, a magistrate, a husband, a teacher, a pupil, etc., it is not in season to hear the Gospel, but the Law. At such a time you are to perform the duties of your profession,” [source]