Therefore learn to distinguish clearly between this article [of faith in Christ] and works. For if this article is lost, then we can fall an easy prey to their [preachers of good works as our means of salvation] deception. They do not know the meaning of faith, but insist that it is of great worth to suffer much, to perform many good deeds, to love God and one’s neighbor, to be pious and obedient. But you must reply: That is all well and good, but it does not make a Christian; nor does it get anyone into heaven. Works are too feeble for that. No, you must say: First I want to become a Christian, and then I will love God and man. Works do not make a person a Christian, but a Christian should perform good works. No one becomes a Christian by means of works. A person becomes a Christian when God grants him grace to come to His Son, Christ, when he is baptized in His name, hears His Word, and accepts Christ in faith. The Christian did not carve out Christ and His grace himself. You contributed nothing to it; you did not fashion, carve, or bake Christ. It is your faith, not your good works. And then the Christian says: I believe in Christ, who was conceived by the Holy Spirit, born of the Virgin Mary; who died, was crucified, and buried; and who rose again on the third day for my sake. Your comfort is that you yourself did nothing at all, that Christ was born, and that He also suffered. These are not our works, and this cannot be acquired by means of works.
Luther’s Works volume 23: Sermons on the Gospel of St. John Chapters 6-8