Our dear Rev. Dr. Martin Luther wrote:
For example, if someone should forcibly take my hand and beat someone to death with it or [in contrast] give alms to the poor, neither work would be mine, even though my hand did it; rather, it would be the work of the one who compelled it to be done. Therefore, that would not harm me or help me at all. So also the works of the Law make no one godly, even though they are done through us. Our will does it only out of the fear and punishment of the law and would much rather do something else, if the compelling and threatening law were not over us. Therefore, they are not our works. Now, each one must be saved through his own works.
Again, if someone does such works not out of fear, as he perhaps thinks, then he still does them because of the promises and enticing of the Law. That is wicked and false, even worse than the former. It is just as if heaven had not been promised and they knew that they would do it all for nothing, then they would not do it. Therefore, again, the works are not our own but of the Law and of its enticing or alluring, through the promise of possessions and reward. These works done for a reward are more dangerous and more difficult to recognize than those done out of fear of punishment, since they are much more subtle and very similar to free, eager, righteous works.
But the works are recognized in the cross when people reject the works of the Law and demand that the works occur for free, without seeking a reward, only for the glory of God and the benefit of the neighbor. Human nature lies defeated and can do nothing; it is found that it does no good works of its own, but only the works of someone else, of the Law, just as an irrational animal runs and works by being beaten or for the sake of its food. How many godly people of honorable character do you think would remain if shame, punishment, hell, or heaven were not before their eyes? No one at all would remain godly, for everything is kept good with fear or profit. Therefore, everything is false and mere lies, as Scripture says, "All mankind are liars and vain" (Psalm 39: 5, 116:11).
So we see these two points in all people. The first is that they are kept by the guardian (the Law) from a disgraceful, shameless, wild life, and remain under the discipline of the works of the Law in an outwardly honorable life. The second is that inwardly in their hearts they truly become hostile to the Law and its punishment, and the more harshly the punishment presses, the more hostile they become. Who is not hostile toward death and hell? But what is this other than being hostile to the Law, which imposes such punishment? But what is being hostile to the Law other than being hostile to righteousness? And what is being hostile to righteousness other than being hostile to God Himself? Here it is definite--is it not?--that we not only are wrong but also hate righteousness, love sin, and are hostile to God with all our hearts, no matter how prettily and honorably our outward conduct in works may glitter.
God certainly wants to be loved with all our heart, as the commandment reads: "You shall love the Lord your God with all your heart, with all your soul, with all your might," etc. (Deut 6:5). God wants all our good works to be our won, not those of the guardian, the Law, death, hell, or heaven. That is, we are to do them not from pure fear of death or hell, not to obtain heaven, but from a free spirit, from a delight and love of righteousness. Whoever does a good work from the fear of death or hell does not do it to the glory of God, but to death and hell. It is a work of death and hell, for they have stolen it, and he does it only for their sakes; otherwise he would not have done it. Therefore, he also remains a slave and servant of death and hell with all such works. But if he remains the servant of death and hell, then he must die and be condemned, as the proverb says, "Whoever is afraid of hell enters it." Likewise: "Trembling does not help against death."
But you say; "What will become of this? Who, then, can be saved? Who is without this fear and trembling before death and hell? Who does his works or leads his good life without this fear?" I answer: Who has loved God if he carries such fear and hatred of His Law and His righteousness within him? Where now is human nature? Where is free will? Will you still not believe how necessary the grace of God is? Will you still not let the behavior of all people be sink false, and untrue? Can you still not be persuaded that works do not make one godly?
Here you can see why the Law is necessary and good and what God seeks with it, namely, these two points. The first is that He keeps us disciplined and drives us outwardly to an honorable life, so that we can live among one another and not devour one another, as would happen if there were no Law, no fear, no punishment, as formerly happened among some heathen. For the same reason, God did not abolish the secular sword in the New Testament, but rather established it, even though He does not want to use it and His people do not need it [Rom. 13:1-7; 1 Peter. 2:13-14]. Rather, He established it so that the shameless and wild people can be restrained, and so that people can live peacefully with one another, support themselves, and increase. Otherwise, all lands would be a wilderness, full of murderers and robbers; no woman or child would remain unravished. Through the sword and His law they are preserved and urged into a quiet, peaceful, and honorable life. Nevertheless, they do not become godly in that way, and their hearts are not at all better. Their hands are only compelled and bound, and the works and righteousness are not their own but come from the sword, which compels this from them and works in them through its punishment and fear.
So God's Law also presses on us and compels us to refrain from much evil because of fear of death and hell, and preserves us like a guardian in an externally honorable life. But no one is godly before God in that way, for the heart remains hostile to such a guardian, hates its punishment, and would rather be free.
The second point is that through the Law the man himself knows how false and unjust his heart is, how far he still is from God, how his human nature is nothing at all, so that he despises his honorable life and knows that it is nothing at all, so that he despises his honorable life and knows that it is nothing compared to what is necessary for fulfilling the Law. Thus he is humbled, crawls to the cross, sighs for Christ, longs for His grace, despairs completely of himself, and places all his confidence on Christ. Christ then gives him a different spirit and changes his heart, so that he never again fears death and hell; never seeks life and heaven; gratis and freely becomes friendly toward the Law; lives in it with a good and certain conscience for dying and for living; and hell, heaven, and all things are of equal value to him.
Thus the Epistle says that Christ freed us who were bound in slavery our whole lives by our fear of death (Hebrews 2:150. Thus he testifies clearly enough that we must be without the fear of death, and all who live in the fear of death are slaves and will never be saved. Now, neither human nature nor the Law can free us from that fear; both of them only increase that fear. Only Christ has freed us from it. When we believe in Him, then He gives us that free, undaunted spirit which fears neither death nor hell, which loves neither life nor heaven, but freely and joyfully serves God.
From this we see, first, how dangerous are the doctrines which drive a man through commandment and Law to the idea that he can become godly through them. In that way they only pull him farther from God, from Christ, even from the Law and all righteousness. They do nothing more than give him an ever more fearful, timid, dejected, and wretched conscience, and always teach him only to fear death and hell, until they drive despair into his heart, so that both here and there he must be the devil's martyr.
Second we see that that is a threefold use of the Law--or that people take a threefold attitude toward it. The first are those who risk everything and lead shameless lives against it; for them, it is a if there were no Law. the second are those who refrain from sch a dissolute life and are preserved in an honorable life; they are under discipline outwardly, but inwardly they are hostile to their guardian, and all their things happen out of fear of death and hell. Thus they keep the Law only outwardly, and the Law keeps them outwardly, but inwardly they do not keep it and are not kept by it. The third are those who keep it outwardly and inwardly; they are the tablets of Moses, written outwardly and inwardly by the finger of God Himself (Exod. 31:18)
(Luther's Works, American Edition. Volume 76. Church Postil II. pp. 4-7)