One of the central narrative arcs in the story cycle of the novels is the movement from polytheism, to henotheism, to monotheism. Most people recognize the first and last terms, but "henotheism" is not nearly as familiar.
So what the heck is it?
Henotheism is the belief that there is one god for a particular people or tribe, without disbelieving in other gods for other peoples. Moses, contrary to popular opinion, was a henotheist, not a monotheist. He did not disbelief in the gods of Egypt -- he said only that they were not for the Hebrews, who were to worship Yahweh and Yahweh alone. That's why the Egyptian priests are able to transform their staffs into serpents. It was a show of the power of their gods. But Yahweh is stronger, and the transformed staff of Moses devours the other two, "proving" that the god of the Hebrews is stronger than the gods of Egypt. A lesson the Pharaoh ignores to his ruin.
In the second novel, The Words of Making, a henotheistic religion arises that greatly alarms the king and the priesthood because of its popularity with the common folk. The men who are in power see the religion of the One God as a subversive force that must be contained or destroyed. The problem for the king is that his son, Gerin, has become a follower of the new religion, since he has come to believe that the divine presence who has appeared to him several times is a messenger of this new god....