Discussing Issues in Shul

Recently in Shul, I began talking about the new movie "The Passion" and my Rabbi suddenly interrupted me and told me that it’s not proper to talk about this issue at Shul. My question is why? Where does it say that you can’t talk about issues at Shul?

If by "in shul" you refer not to a foyer or a Kiddush room but to the place where you daven, you should refrain from almost every non- Torani discussion there. The violation is even more serious if people talk during davening- a common but still serious infraction both of Halacha and of decorum.