What is the theme in Children of God: A Novel by Mary Doria Russell?

Religion fills Mary Doria Russell's novel Children of God. The book features two protagonists on separate worlds. Emilio Sandoz is a self-described apostate Roman Catholic priest on the verge of marrying when he is kidnapped by Jesuits with the Pope's approval and sent back to the planet where he has been mutilated and raped. The other is a Sephardic Jew who survives as a young orphan on Earth as a prostitute and then on the planet Rakhat for forty years living among hunted Runa refugees and a few Jana'ata, who have sworn off eating Runa.