A character’s religious beliefs and practises can show more about them than anything else. These can direct the character’s actions and reactions. Lock them into a dilemma, a battle that adds to the story.
Characters need personal boundaries and rules in order to be believed. Everyone has that line in the sand they won’t, maybe, cross.
I have no problem with religion in my fictional reading. There have been times I’ve enjoyed the story more because of this element. I don’t even mind preachy characters. They exist in real life and make for interesting characters. I don’t even mind if the author is religious and this is how they prefer to write. We all write to our personal limits. We can use our writing to showcase our faith.
However, I don’t want to be preached to by the author. Fictional writing can be a vehicle to share, but it’s a fine line and the author should watch or they risk overstepping and end up expressing themselves and not the characters.
Then again isn’t all writing a fine line and we, the readers, decide if it has been crossed?