There's a hypothesis (don't recall how it's called in English), that says that a religious object can hurt/repell vampires, because other people believe in the holy aspects of said object. That it's not the object itself, but the belief itself, that makes the object a weapon against vampires.

Interesting! It also seems to hold over time. I'm thinking of Divia trapped in the Egyptian tomb. I'm assuming the applicable religion and attendant believers died out long ago, but she couldn't escape until the grave robbers broke the religious symbol on the sarcophagus

I'd disregard the "the vampire has a split personality and thus can forget she's a vampire" episode, because... come on... just nope.

LOL! Fair enough, but I shall not disregard because state of mind is my favorite theory! I gotta take what I can get.

Maybe he didn't really believe that Nick was possessed by a demon in SOB, but he could have thought that he needs to encourage Nick, so he can "fight the demon" with this mindset. I bet he would have said about anything to save Nick

Save Nick from what though?