In a letter dated June 8, 1944, Bonhoeffer put it this way:
The movement that began about the thirteenth century (I'm not going to get involved in any argument about the exact date) towards the autonomy of man (in which I should include the discovery of laws by which the world lives and deals with itself in science, social and political matters, art, ethics, and religion) has in our time reached an undoubted completion. Man has learnt to deal with himself in all questions of importance without recourse to the "working hypothesis" called "God." In questions of science, art, and ethics this has become an understood thing at which one now hardly dares to tilt. But for the last hundred years or so it has also become increasingly true of religious questions; it is becoming evident that everything gets along without "God"--and, in fact, just as well as before. As in the scientific field, so in human affairs generally, "God" is being pushed more and more out of life, losing more and more ground.