A Conreligious Detail: Competition for the Priesthood as Source of Scripture

Consider a religion where a number of families have some kind of legitimate claim to the position of high priest. Being the high-priest family brings perks beside status: it gives some right of taxation of the population.

Consider if such a religion is rather conservative with regards to its ritual: even the slightest change could be seen as invalidating a priest's legitimacy, and therefore also forcing the current family of the high priest to abdicate from their position.

Pointing out these changes requires good memory, though, and if there's daily rituals (with different details for almost every day), an attempt at calling someone out for changed rituals requires a great deal of knowledge as well as the resources to keep a person posted at the temple scrutinizing the activities of the high priest and his attendant clergy (from his tribe, obviously). So, only competing families that currently are fairly well of could post someone there, and even have the records that codify what has previously been observed.

Originally, different families may have their own codifications. Disputes as to what are the accurate codifications may arise. Some kind of arbitration process between different codifications arises, and slowly leads to a consensus version.

The scripture has little to no impact on the life of the regular believer, but for a handful of families, it is an important political tool. Not all these families can keep observers constantly, so attempts every few years might occur - a family might have a particularly observant (and literate) son, and figure that this year he's not needed on the fields, this might be a chance to the priesthood. Might be that some certain particular rituals of importance are more likely than others to go wrong, so when the high priest is getting old and more likely to misspeak something due to frailty, representatives of several families show up at all the days of difficult rituals. Of course, the priestly family also has its own reader there, following along so as to prevent false accusations of infidelity to the text.

Over time, language changes but the texts do not, and during several years it might be possible that only a few token readers have appeared on a few days. Thus, there is a possibility that sacrificial rituals which are carried out by learned rote no longer fit with how people understand the codified text - the term for some body part of an animal has changed, and now the sacrifice is carried out in a way that disagrees with the language. Terms for movements change, and suddenly a certain invocation done with a certain movement is invalid.