Poor Stephen is so much less powerful than Iscariot thinks he is. The Vatican is thinking “expertly guarded vampire stronghold with hordes of loyal mesmerized followers”, when in fact Stephen barely knows how to use his powers, and his only defense is Jon plus basic-cable security.
Stephen: I’m not here!
Sister Kim: Funny…that’s what your secretary told me. Did he know what you are? Did you promise him eternal life in exchange for risking his to protect you?
Stephen: No! I promised him a nearly-average salary and as many free Colbert Nation T-shirts as he could sew!
Sister Kim: Lying will not save you, monster. [KRACK] The justice of the LORD has come!
Stephen: Just hang on, Stephen. I’m coming! And don’t eat anybody before I get there!