Was that thing a vampire or an angel? Seems like they were all turned into vampires, but their strong religious beliefs blinded them into thinking the creature is an angel and they are God’s soldiers.
It was a vampire. Father Paul erroneously took the gifts of the vampire blood as the blessing/healing of his ailments and identified it as an angel. He also felt it could help the people of Crockett Island and save their eroding community which the vampire exploited as a way out of its old tomb which was long lost in the desert of the holy land. It wasn’t until the entire island was infected or turned that Father Paul realized the errors in his ways/blind faith.