I question the reasoning for my friend's religious beliefs.
What makes you question your friend about this?
I saw him buying books on witchcraft and I know he only did it to get laid.
I understand where you're coming from, but you still shouldn't question your friend's religious beliefs. They may think you're rude if you do that and there is a chance you might not be correct.
Fuck them, it's my choice whether I question or not. Who knows maybe they'll learn from it anyway.
Questioning your friend's religion doesn't seem right in this situation and I think that you should just leave it alone. Will interfering and making this an issue benefit anyone?