Most human nations in Scarterra use a variation of the feudal system for government. Most feudal lords want to have powerful divine spell casters that are loyal to them and they want the legitimacy of being in the Nine's good's graces (or at least appearing that way to the populace. One way that some choose to obtain this is to establish feudal bishoprics. To establish a feudal bishopric, a king (or less commonly a duke or a count) will bestow a piece of land to a priesthood. The priesthood is allowed to oversee the day-to-day activities of that piece of land and rule over the peasantry there deriving income from the crops, timber, minerals, fish, or reagents produced on that land. Traditional feudal rulers owe their lieges military services, money, or both. Feudal bishoprics owe their liege magical and religious services instead of or in addition to the usual payment to one's lord. Feudal covens are usually free to select their leader via any means they want. Usually via the priesthood's normal system of ranks though multi-priesthood bishoprics often have very complicated systems of selecting their collective leader usually involving a ruling council with a rotating spoke person. Like most feudal contracts, feudal bishoprics are generally meant to operate in perpetuity with the bishopric continually answering to their lord's heir after their liege dies and the bishopric electing a new leader every time the previous leader dies.
Most Bishoprics are fairly small, on par with that of a barony. Some rulers seek to have many small bishoprics, with separate bishoprics for different deity's priesthoods. Other times they might have two or three priesthoods run the same bishopric collectively (presuming the priesthoods are on good terms with each other. While rare, these types of bishops tend to wield a lot of power and control land on par with most dukes. It is very rare for lords to ever require monetary taxes from their bishopric vassals. More often than not, the lords are giving their vassals money in the forms of donations.