This can best be classified as theological fiction. They totally wipe out all other religions.
Mankind then makes contact with an other race, who has FTL spaceships.
Their religion is based on the fact that when you travel faster than light, you sort of hallicunate, whereby you can commune with god. Also, they claim all other gods are 'imperfect aspects' of their own. Because of this, some worlds split off from Earth. Many prophets of this 'new' religion appear. The Earth church tries to 'help' one of them to be the 'real' one, so they later can spectacularily destroy him, helping putting down foreign ideas.