What are the motifs in God Emperor of Dune by Frank Herbert?

Religion is a recurring idea. By the time of God Emperor of Dune, the institutional Priesthood is undergoing no significant changes, but the religious aspect of the Fish Speakers, Leto II's chief devotees, is decreasing. Nayla is the consummate believer in Leto II's divinity, but he tells her he is not creating a religion; he is the religion.