... There is .. in Bonhoeffer’s vision of the world come of age, a rejection of religion as salvation either by transmitting the individual to some protected religious realm, or even as protection from something that, without religion, a man might fall into, like despair or self-righteousness. Put more clearly, Bonhoeffer states that in the world come of age, we can no longer be religious, if religion is defined as that system that treats God or the gods as need-fulfillers and problem-solvers ...
The plea for a religionless Christianity is thus a plea to give up all claims for the necessity of religion generally. Christianity -- as would be true of any religion and any irreligion -- is not necessary. It is merely one of the possibilities available to man in a competitive and pluralistic spiritual situation today. Christians are perfectly free to offer their wares to the world come of age, the religionless world. But they have no head starts, ontological or psychological. This in turn implies no clergy deductions, no tax exemption and no preferential treatment of any kind. Finally, when men say "no" to Christianity, it is a real "no," and not a deeply concealed "yes" masked under a protest against false religion. There are those, Bonhoeffer says, who can make it today without God and without despair and guilt. And their success is just as real as the fulfillment of those who live happily and have a God.
We can begin to see what Bonhoeffer is doing and persuading us to do. He is undermining the traditional Christian confidence in language, argument, debate; in short, our assurance that we can persuade an indifferent world that it really needs God. He is forcing us to shift our center of attention from theology, apologetics, criticism of culture, the problem of communication, and even from hermeneutics, to the shape and quality of our lives. He has enabled us to note, in Protestantism, perhaps he has even brought about, the end of theological confidence, and the beginning of a time of confusion between theology and ethics. The communication of the Christian in our world is likely to be, at least for a time, essentially ethical and nonverbal. Christians themselves, at work in the world of the twentieth century, saying their "yes" to it as vigorously as possible, provide the dynamic evidence for the truth or falsity of their message.
The time when the real vitality of Protestantism was intellectual and centered in the Academy is at an end. The Protestant continues to engage his unbelieving brother, but he is likely to be engaging him by working alongside him. What distinguishes this Christian from his non-Christian comrade? If there is any answer to that, it may well be found by meditating on the third, and most elusively powerful, of Bonhoeffer’s ideas, written nine months before he was hanged: "Man is challenged to participate in the sufferings of God at the hands of a godless world."
http://www.religion-online.org/showchapter.asp?title=537&C=591