Gurkhal
Auror
Definitely look at monotheistic religions other than Christianity. Off the top of my head I can think of Judaism, Islam, Baha'i, Rastafarianism, Sikhism, and Zoroastrianism. There's a lot of variety in there to start with, and once you have an idea of what you want your imagination is what will set the result apart from your source material.
I agree personally. My primary reason to focus on Christianity is because that was what OP talked about in his original post as wanting something close to the medieval church,by which I kind of assume that he meant the medieval Catholic church.