In the second chapter of Nachfolge (Discipleship), Bonhoeffer has some incredible things to say about the Law and the Gospel–Incredible coming from a Lutheran.
Perhaps the most thought provoking statement nugget is
The call to discipleship is a commitment solely to the person of Jesus . . . It is beyond enmity between law and gospel. Christ calls; the disciple follows. That is grace and commandment in one (59).
What a wonderfully beautiful way to express the unity of the law and grace! This then is the foundation of his well-known twin statement later in the chapter:
Nur der Glaubende ist gehorsam, und nur der Gehorsame glaubt/ Only the believer is obedient, and only the obedient believes (52)