"Christianity changed the ground of human identity. It was able to do that because of the way it combined Jewish monotheism with an abstract universalism that had roots in later Greek philosophy. By emphasizing the moral equality of humans, quite apart from any social roles they might occupy, Christianity changed ‘the name of the game’. Social rules became secondary. They followed and, in a crucial sense, had to be understood as subordinate to a God-given human identity, something all humans share equally. Thus, humans were to live in ‘two cities’ at the same time."