The Ori religion, developed so that those beneath may follow and worship them in accordance to their wishes. A centerpiece of this faith is fire, the very element the Ori reside within in the Flames of Enlightenment.
Origin is explained in the Book of Origin, carried by all who believe in the faith. Priors are dispatched to regions in the cosmos where there are nonbelievers and those who have never-before encountered the belief system. Eventually they are either converted or destroyed.
Avalon, Part 2 - Daniel and Vala begin to learn about Origin and the consequences for not following in its teachings.
Origin - A Prior takes Daniel and Vala to the city of Celestis, where Daniel is granted an audience with the Doci who explains Origin and its doctrine.
Line in the Sand - Tomin begins to question his faith when he realizes that a Prior is interpreting Origin to mean what he wants it to mean.
Stargate: The Ark of Truth - Origin is challenged when the energy from the Ark of Truth washes over the faithful throughout two galaxies, showing many millions of followers the truth about what the Ori are.