The biggest player I know of in fiction written for a specific belief system is "Christian Fiction," which is a real thing, and a very large market.
I'm not a Christian (Buddhist; very different thing) but I have read some fiction dubbed "Men's Fiction" which crossed over into "Christian Fiction" because the protagonists were devout Protestant-type American Christians.
After a few chapters of butch blowing things up and chest-thumping I realized that all these Seals, Rangers and SAS fellows were calling on Jesus all the time, and praying to the Christian deity constantly.
While the conflation of patriotism with this brand of Christianity is a damned lie, I didn't mind the protagonist being a Christian and practicing his faith, because that is who he is.
I could like him as a character, understand his motivations, and follow his adventures in his universe (all boys all the time, but none of them are gay and all of them are a particular kind of Christian) because the adventure story was well plotted and well written.
We read fiction to be entertained, to escape our own worlds, to have adventures in times and places about which we can only otherwise dream. Why shouldn't those characters have belief systems different from our own? Are our own faiths so weak that we can't look at the world through someone else's eyes and learn about how other people see the world?
Go ahead. Read something. See something. Learn something.
Give a book, and give a world.