This is not about religion, it’s about Gothic horror in a setting rife with people making deals with demons.
How cool is it to have a character who has a familiar, but is not a wizard? Here’s a witch. Have some cool extra powers. But there is a price, down the road. A highly customizable system that meshes with dark secrets and darker fates makes magic available to non-spellcasters through demonic pacts. Good times, am I right?!