God is dead in the hearts of modern man. Killed by both science and rationalism.. . It should be noted that it really wasn't a slogan of Nietzsche, though. It was the words of a 'madman' (Zarathustra, I think) that nobody listened to. Nevertheless, the idea is that modern man hasn't realized yet that we have 'killed' God ... not literally, but figuratively ... making God less important in the universe and our lives by new science, philosophical thought, and ethical standards.