When talking about topics that are very important to people like religion, there is no need to lose friends just because you disagree with them. Be respectful. Say things like:
“I understand your point of view, but I disagree with the reasons you give fo what you think.”
Be open to changing your mind if your friend presents good evidence. If all you are doing is trying to be right no matter where the discussion goes (A Right Fighter), that’s not really a very meaningful conversation.
If the discussion gets too heated, change the topic and agree to disagree for now with the plan to pick up the conversation again later when both of you have calmed down and are thinking more clearly.