The twelfth (and second to last) manuscript in Bonhoeffer's Ethics is entitled The "Ethical" and the "Christian" as a Topic, which is perhaps not the most catchy title ever conceived. It attempts to approach the question of "whether and to what extent the 'ethical' and the 'Christian' can be treated as a topic at all" (363), which seems a somewhat belated concern - one wonders whether, had he lived, Bonhoeffer might have placed this section rather nearer to the beginning. Then again, its content builds on much that has gone before, so perhaps not.
There is a lot in this brief chapter, including some fascinating and controversial material about the need for an 'above' and a 'below' in society if there is to be ordered ethical discourse. But the heart of the chapter, it seems to me, is the contrast between ethics and God's commandment. One reason that ethics often seems a dubious subject, according to Bonhoeffer, is that "the ethical phenomenon is a boundary event both in its content and as an experience" (366). That is to say, ethics does not deal with the ordinary and the everyday, but only with the limits of human behaviour. It is therefore always an interruption to human life, confronting it with a limit that ought not to be transgressed. Because this is so, ethics cannot become an everyday phenomenon - it just isn't the case that people live in a constant stream of ethical dilemmas, always standing at the crossroads of good and evil. If ethics does seek to become more than a boundary discipline, it degenerates into tedious moralism.
By contrast, "the commandment of God is the total and concrete claim of human beings by the merciful and holy God in Jesus Christ" (378). "It does not merely guard, like the ethical, the boundaries of life that must not be crossed, but it is at the same time the center and fullness of life" (381). "The commandment of God is permission to live before God as a human being" (382). God's command, which always comes to a particular person in a particular time and place who stands in particular relations of responsibility and obligation, is always permission as well as limitation.
As a striking example of what he means, Bonhoeffer refers to marriage. "Only when the commandment not only threatens me as a transgressor of the boundaries but also convinces me and wins me over by its actual content does it free me from the anxiety and uncertainty when making a decision. When I love my wife and affirm marriage as instituted by God, then my marriage acquires an inner freedom and a confidence of how to live that no longer suspiciously observes every step I make nor calls my every action into question. The divine prohibition of adultery is then no longer the focal point of all I think and do in my marriage - as if the meaning and purpose of marriage consisted in avoiding adultery!" (382).
Love for God's commandment sets us free to actually live with confidence; ethics only erects nervous boundaries at the edges of life. The latter may be necessary, especially in disordered times, but the former is comprehensive. We live, not by a code of ethics, but by God's commandment spoken to us - to me, to you - in Jesus Christ today.