How can we escape if we neglect so great a salvation?
“In the Law there are very many works—they are all external—but in the Gospel there is only one work—it is internal—which is faith. Therefore the works of the Law bring about external righteousness; the works of faith bring about righteousness that is hidden in God. Consequently, when the Jews asked in John 6:28: ‘What must we do, to be doing the works of God?’ Christ draws them away from a large number of works and reduces the works to one. He says: ‘This is the work of God, that you believe in Him whom He has sent’ (John 6:29). Therefore, the whole substance of the new law and its righteousness is that one and only faith in Christ.
Yet it is not so one-and-only and so sterile as human opinions are, for Christ lives. Not only lives but works, and not only works but reigns. Therefore it is impossible for faith in Him to be idle. It is alive, and it itself works and triumphs, and in this way works flow forth spontaneously from faith. For in this way our patience flows from the patience of Christ, and our humility from His, and the other good works in like manner, provided that we believe firmly that He has done all these things for us, not only for us but also before our eyes, that is as St. Augustine is wont to say, not only as a sacrament but also as an example.”
“Lectures on Hebrews” (1517-18)
Luther’s Works 29, 123