God is dead. God remains dead. And we have killed him. How shall we comfort ourselves, the murderers of all murderers? What was holiest and mightiest of all that the world has yet owned has bled to death under our knives: who will wipe this blood off us? What water is there for us to clean ourselves? What festivals of atonement, what sacred games shall we have to invent? Is not the greatness of this deed too great for us? Must we ourselves not become gods simply to appear worthy of it?
Nietzsche, The Gay Science (section 125 “The Madman”)
Here is a possible explanation of how Mr Nietzsche meant what he expressed in those lines above. Of course he is not expressing his belief in the actual death of a real deity as he was most likely atheist at heart. Rather, he is expressing lament and fear that the world is turning away from an objective foundation for morality.
Ethical behavior before the Renaissance was dominated by the idea that God was the origin and giver of all morality. But due to the ‘success of science’ philosophers became enticed with ‘scienticism’ and almost en masse started preaching ethics derived from ‘logic’ (e.g. Kant and Hegel).
This meant the end to God’s role as the father of morality. Because, he argued, people no longer believe in God they can no longer recognize absolutes with respect to morality. He was not a moral relativist, he is not arguing there are no absolutes with respect to morality. He is railing against the rise of moral relativism and nihilism. Nietzsche’s realization that faith in God could not survive as the basis for morality and his fear that the loss of faith would lead to widespread nihilism is what pushed him to search for a more reliable, fundamental, basis for objective morality, which he eventually developed into his theories on the will to power.