All religions, with their gods, their demigods, and their prophets, their messiahs and their saints, were created by the credulous fancy of men who had not attained the full development and full possession of their faculties. Consequently, the religious heaven is nothing but a mirage in which man, exalted by ignorance and faith, discovers his own image, but enlarged and reversed — that is, divinized. The history of religion, of the birth, grandeur, and decline of the gods who have succeeded one another in human belief, is nothing, therefore, but the development of the collective intelligence and conscience of mankind.

God and the State (1871; publ. 1882)