Luther feels that it is easier to visualize the Christian’s way when two truths are taken into consideration: 1) The Christian must not remain in his sins; yet in spite of this 2) the Christian remains a sinner. These two statements seem to contradict each other. The peculiar nature of the Christian faith is found, according to Luther, in this apparently irresolvable contradiction. He who lives in faith in God and Christ strives with all his powers to be free from sin. Yet he knows that there is sin in him. In fact, the more vital one’s faith the more clearly he sees the sin that still clings to him.
Already in the first lectures on the Psalms Luther notes that to the extent that man does not desire to become better he ceases to be good. He who is righteous, let him be righteous still (Revelation 22:11), and let him who stands beware lest he fall (1 Corinthians 10:12). Luther places much emphasis on Ecclesiasticus 18:7, which states that “when a man has finished, he is then only at the beginning.”
In Paul’s theology the man who in Christ has already reached the goal must continue with the race. The reason for this is that the Christian lives under the conditions of two ages (aeons). The old and new ages alike condition him. Likewise in Luther’s theology the Christian is ever en route, inasmuch as he is simultaneously righteous and sinful. Only the saints in heaven can relax and enter fully into their possessions. In Luther’s early evangelical theology Augustine’s influence was very strong, and so we find there statements which interpret sanctification as a progressive series of events. His later theology however shows a distinct aversion to all detailed scrutinizing of holy living. It is difficult to speak of progress, for there is no such thing as growth of the old man in holiness and perfection. The old man in us must be put to death daily and the new man arise, as the Small Catechism puts it. Our natural life is the life of the old man. No form of cure will make the old man into the new. It remains old to the very end. As Luther sees it, the Christian must judge himself once and for all. The new man lives in us only as the alien righteousness of Christ. This righteousness never changes into a part of my personality (ego). If in our quest for such change we turn our eyes upon ourselves, we become “self-righteous servants of the law.” The new in us is Christ himself. But under the conditions of this present life Christ does not control us so completely as to make it unnecessary for the old man to go through daily mortification. The new man never becomes a creature whom we might touch and see.
From a certain viewpoint Luther’s teaching placed all outward piety under suspicion. In any given moment piety can by, as [Regin] Prenter notes, an expression of the Spirit or of the flesh, according to whether the man in that particular moment is either Spirit or flesh. One cannot therefore speak of unambiguous growth toward genuine righteousness. Prenter is undoubtedly right when he says:
When Luther speaks about the progress of sanctification, he thinks of something entirely different. He thinks of the fact that man on the way between baptism and resurrection constantly and anew takes leave of himself to take refuge in Christ’s alien righteousness. In this refuge of faith in Christ, man is Spirit, new man, and all his past life is at once considered as flesh, as old man. In this manner the Spirit, who knows only Christ’s alien righteousness, is constantly struggling against the flesh, which wants to hold on to its own past life as an appropriation, its own righteousness. In the resurrection man shall be completely Spirit. Then the Spirit shall no longer struggle against the flesh. But on the way between baptism and resurrection man is Spirit and flesh (Spiritus Creator, pages 69-70).
In the evaluation of holiness all that is outward must be suspect. No visible piety or concrete act as such guarantees that the mind or attitude itself is holy. On the contrary, with progress there is regress. In becoming better the Christian becomes worse. To reach the goal is to start all over again. Luther was quite aware that all this made no sense to man’s wisdom, to the “sophists.” That the Christian is simultaneously a sinner and a saint is contrary to reason. The human ideal is that life be altogether without sin. As a demand this ideal drives men into despair.
Lennart Pinomaa, “Faith Victorious: An Introduction to Luther’s Theology”, pages 67-69