As I understand it, some mighty weapon is hidden in St. Orthenius's Tomb. And to open it, I need 3 angel statuttes. I tried just opening it myself, and I tried to give them to Jad-Habaal spy so he could open it for me. But I still can't enter.
Maybe I skipped some section of that plot? I think it is too early for me to go there, because when I found the last statuette in Alvaron, Pontifex took it from me. I reloaded and ran away with the statuette before Pontifex could talk to me.