I think monotheism has been around for a very, very long time. The Hindu religion, although it appears to outsiders to be a pantheon of many gods and goddesses is actually a religion which recognizes One transcendent Divine above all the gods and goddesses. The gods and goddesses merely represent the different aspects of the One Divine. They are symbolic of those aspects, like facets of one diamond. They serve a rather similar purpose to the many saints and Angelic figures in the Christian faith.

Hinduism is very ancient, I think moreso than the teachings of Moses and Abraham.

In any case, people have always tended to assume there is an ultimate Truth...and that to know it would be to have complete knowledge and wisdom.

To posit one transcendent God is simply to personify that Truth and clothe it in somewhat human terms that ordinary people can relate to. I believe that's part of what Slag was saying.