Manuscript four of Bonhoeffer's Ethics is entitled Guilt, Justification, Renewal. This really is a Christian, which is to say a theological, ethics - the good news of Christ is not incidental to the question of what we ought to do (and not do). The important context here is Bonhoeffer's reading of the history of the West.
We begin with Christ: "The issue is the process by which Christ takes form among us." (134) Because that is what is needed in the moral chaos of the collapsed post-Christian West. We need to know "the real, judged, and renewed human being" - but this human being "exists only in the form of Jesus Christ, and therefore in being conformed to Christ" (134). There is no way around Jesus Christ here: to be assumed by Christ in his incarnation; to be judged in Christ at the cross; to be joined with Christ in his resurrection - that is real, judged, renewed humanity, and it is the only way forward.
But as well as being the only way forward, this represents for the wayward West a major turning back - back to its Christian heritage, because back to Christ. And "there is only one way to turn back, and that is acknowledgement of guilt toward Christ" (135). This acknowledgement of guilt is not about confessing our occasional and more-or-less serious failures and declensions, but it is acknowledging our falling away from Christ. That is the miracle - fellowship with Christ, the taking form of Christ among us, happens as we together confess that we have fallen away from this fellowship and this form. This acknowledgement of guilt is based on the gospel - "only on the grace of Christ, because of Christ's reaching out for those who have fallen" (135).
So far, Bonhoeffer is talking about the collective guilt of the West - but where will this confession occur? Only in the church. "It is tautological to say that the church is the place where guilt is acknowledged. If it were otherwise, the church would no longer be the church" (135). The church takes on and confesses not only its own personal and corporate sin and failure, but also the whole falling away of society. The church confesses sin, all sin - "This confession is strictly exclusive in that it takes all guilt upon itself" (136) - yes, all guilt. There is a parallel to the action of Christ here: "Christ conquers us never more strongly than by completely and unconditionally taking on our guilt and declaring it his own, letting us go free. Looking on this grace of Christ frees us completely from looking at the guilt of others and brings Christians to fall on their knees before Christ with the confession: mea culpa, mea culpa, mea maxima culpa" (136).
Bonhoeffer continues with a series of concrete confessions. One which particularly strikes me is this: "The church confesses that it has coveted security, tranquillity, peace, property, and honor to which it has no claim, and therefore has not bridled human covetousness, but promoted it" (140). Ouch. (See another one here).
Bonhoeffer's notion of original sin plays in here: in confession I acknowledge "my sin as the origin of all sin, as, in the words of the Bible, the sin of Adam" (137). I am guilty of all sin; my sin is the source and original of all evil. I don't look around for the guilty one - I am the man. Therefore I can in all seriousness confess sin and guilt, and thus be justified and renewed through Christ.
This is in the church. Society per se cannot experience this sort of repentance and renewal. "For the church and for individual believers there can only be a full break with guilt and a new beginning, through the gift of forgiveness of sin. But in the historical life of nations there can only be a slow process of healing" (143). Concretely, for the West, this slow process of healing must mean amongst other things "giving space among the nations to the church of Jesus Christ, the origin of all forgiveness, justification, and renewal" (145). This is not an arrogant claim for the church; it is simply a realistic claim if the real, judged, renewed humanity is seen in Christ alone, who takes form in his community.