For Bonhoeffer, the relationship with God ordered everything else around it. A number of times he referred to the relationship with Jesus Christ as being like the cantus firmus of a piece of music. All the other parts of the music referred to it, and it held them together. To be true to God in the deepest way meant having such a relationship with him that one did not live legalistically by "rules" or "principles." One could never separate one's actions from one's relationship to God. It was a more demanding and more mature level of obedience, and Bonhoeffer had come to see that the evil of Hitler was forcing Christians to go deeper in their obedience, to think harder about what God was asking. Legalistic religion was being shown to be utterly inadequate.
Eric Metaxas, Bonhoeffer: Pastor, Martyr, Prophet, Spy
obedience, principles