So I have this character, She has this set of cards -- Tarot cards -- and she keeps trying to foresee the future with them. She would pull it off if only she interpreted them right. So I'm having fun with it and then it occurs to me. . . .
Have I boxed myself in?
There's a lot of denial about Tarot cards in many circles, first about their recent origin and second (and more relevantly here) about their symbolism. You see writers trying to paper over the cards The Pope (who is often rendered the Hierophant or otherwise rendered innocuous for revealing its origin) and still more over the card Judgment, showing the archangel blasting the trumpet on the last day and rousing the dead from their graves.
Whether it is approved of and regarded as part of the duties of a priest, or disapproved of and treated as impiety, there is always a magical fringe about the edges of religion, where people try to put it to work for short term and practical effect. And the Tarot cards were part of the fringe of Christian religion. Yeah, they drew on other themes, being boundless syncretistic. But they didn't exclude Christianity.
So, did I make a world-building decision about the religion of this world? Hmm. . . hmm. . . I have made it clear with her thoughts and her sneaking that it's not approved of. Or perhaps I could excise it, since it's a subplot. Or perhaps I could muddy up the imagery like so many other writers. . . decisions, decisions.