Martin Luther, commenting on Galatians 5:17:
Thus there is great comfort for the faithful in this teaching of Paul’s because they know that they have partly flesh and partly Spirit, but in such a way that the Spirit rules and the flesh is subordinated, that righteousness is supreme and sin is a servant. Otherwise someone who is not aware of this will be completely overwhelmed by a spirit of sadness and will despair. But for someone who knows this doctrine and uses it properly even evil will have to cooperate for good. For when his flesh impels him to sin, he is aroused and incited to seek forgiveness of sins through Christ and to embrace the righteousness of faith, which he would otherwise not have regarded as so important or yearned for with such intensity. And so it is very beneficial if we sometimes become aware of the evil of our nature and our flesh, because in this way we aroused and stirred up to have faith and to call upon Christ. Through such an opportunity a Christian becomes a skillful artisan and a wonderful creator, who can make joy out of sadness, comfort out of terror, righteousness out of sin, and life out of death, when he restrains his flesh for this purpose, brings it into submission, and subjects it to the Spirit.
Luther’s Works, volume 27 “Lectures on Galatians 1535.Chapters 5-6; 1519.Chapters 1-6” page 74