The first, highest, and most precious of all good works is faith in Christ, and as it says in John 6 [:28–29], when the Jews asked him, “What must we do, to be doing the good work of God?” Jesus answered, “This is the good work of God, that you believe in him whom he has sent.” Now when we hear that or even preach it, we pass over it: we think nothing of it and think it easy to do, but actually we ought to pause a long time and think it over properly. For in this work all good works exist, and from faith these works receive a borrowed goodness. We must make this absolutely clear, so that men can understand it.

Martin Luther, Treatise on Good Works (1520), in Luther’s Works, vol. 44, No. 1 (The Christian in Society), pp. 23–24. American edition.