"Small Gods by Terry Pratchett. It changed my outlook on life and religion....love it."
-Plot background
Omnia is a theocracy based on the Seven Books of the Prophets of Om, collectively known as the Septateuch. The Discworld is flat and is orbited by its sun, but Omnian doctrine says that the world is round and orbits the sun. Omnians believe in a single god, Om, though the Discworld has many gods, including the billions of Small Gods who exist as points of desire searching for believers. Om was once a Small God, but managed to speak to a shepherd, gained believers (despite the shepherd being stoned to death) and took over from Ur-Gilash as the God of what became Omnia. In Omnian tradition there is a new Prophet every two hundred years.
While Brutha, Vorbis, and Om are in the desert, the Tyrant of Ephebe manages to regain control of the city and contacts other nations who have been troubled by Omnia's imperialistic ambitions. Sergeant Simony, whose native Istanzia had been conquered by Omnia in his youth, brings Didactylos and Urn to Omnia to lead the Turtle Movement in a rebellion against the Church.