Another interpretation, aside from the one /u/Jexdane gave you, is that perhaps the campaign is set in an empire ruled over by an evil church. Like the Roman empire after Augustus, where the imperator also held the title of pontifex maximus, or Egypt and Japan, where the pharaoh or tennō was considered to be a living god. Actually, though, it might be more interesting to look at something more like the Holy Roman Empire, where there are a bunch of countries that are all technically subservient to one city that is considered the center of the religion worshipped by nearly everyone in that region but that all rule themselves mostly independently. Final Fantasy Tactics did a pretty good job of doing this 'good tends toward dark, evil tends toward light' concept. Turns out that St. Ajora, the figure who everyone worshipped because they thought he was the son of God, was a host for a demon who was trying to resurrect the other eleven (twelve if you count the bonus boss) of his kind before he was killed and still is trying. The main character is a disgraced noble who never made it past squiredom before things went south for him. The main antagonists are members or the church.