For me, being a historian of religion has made me very skeptical of claims that modern people make like "Judaism teaches x" or "According to Christianity, no one may do y." Because for most claims like that, the important people associated with the religion said pretty much the opposite at some point in their history. History has taught me that "Christianity says," functionally, means "Christians say." And people have beautiful crazy complicated different lives, so they say beautiful crazy complicated different things.

It's also helped me really understand that, for most people, religious statements aren't truth-apt propositions. Understanding the all-encompassing nature of medieval religion helped me understand that, for me and the people around me, religion is a way of life, not a system of proofs. I sort of knew that before, but it's easier to understand when you study people who have religious practices that seem kind of absurd to us but that make total sense to them. They're not stupid, they're just having a different conversation.

Here's a similar question I asked a while ago, and received an amazing reply from /u/sowser.