From Prof. Sean Kelly's Navigating Past Nihilism (h/t, reader BL):
“God is dead,” Nietzsche wrote in a famous passage from “The Gay Science.” “God remains dead. And we have killed him.”
There is much debate about the meaning of Nietzsche’s famous claim, and I will not attempt to settle that scholarly dispute here. But at least one of the things that Nietzsche could have meant is that the social role that the Judeo-Christian God plays in our culture is radically different from the one he has traditionally played in prior epochs of the West. For it used to be the case in the European Middle Ages for example ─ that the mainstream of society was grounded so firmly in its Christian beliefs that someone who did not share those beliefs could therefore not be taken seriously as living an even potentially admirable life.