The command to you is not to crawl into a corner or into the desert, but to run out, if that is where you have been, and to offer your hands and your feet and your whole body, and to wager everything you have and can do. What is required is a hunger and thirst for righteousness that can never be curbed or stopped or sated, one that looks for nothing and cares for nothing except the accomplishment and maintenance of the right, despising everything that hinders this end. If you cannot make the world completely pious, then do what you can.
The Sermon on the Mount, trans. Jaroslav Pelikan: in vol. 21 of Luther’s works, Concordia, 1956.