To sort of go off of what [@Vilageidiotx] said about Catholicism vs Protestantism: in how I've perceived the Protestant-Catholic split, the Protestant churches didn't do much to adopt the cosmology of the Catholic Church, or I've never seen it as being as prominent or widely spoken of. Like in my time as a Presbyterian no one every went on and on about the Archangel Micheal or Gabriel in Sunday School and at sermon.

Of course, I also never really attended a Catholic sermon, so I can't compare. Neither have I ever attended an Episcopalian or Baptist sermon.

But I think if you're going to do anything with the Protestant field then the obvious best framework for that would be the Thirty Years War or some crazy history nerd shit me and Vilage would whip our dicks out too. I don't know of anything seriously heavy in mysticism outside of Appalachian Christianity in the Protestant fields.

Or alternatively if you still need it a world theme then any setting where-in individual reading and interpretation of the bible or some shit is important. But fuck if I know. Going back on what Vilage said John Milton and Dante is probably your best and most straight-forward reference to an RP based on Christian magic and mythology which defaults you to the realm of the Catholic hierarchy. 

Arguably you may be able to find something in the Eastern (Greek/Russian/Armenian/Georgian) Orthodox Church, but that implies you're having faith in people wanting to be Greek, Slavs, Georgians, or Armenians; which also has a relatively simplified hierarchical structure (at least on Earth, where all bishops are equal in rank among their peers and there's no supreme bishop like the Pope, what there may be is largely nominal or exists because of close inter-relation with the supreme secular monarch/ruler of the realm).