In this story by Ben Edlund we meet a vampire who use to be a priest back during the Spanish inquisition. He burned a real witch at the stake and a friend of hers who happened to be a vampire killed all of his friends and turned him into a vampire.
At first he was disturbed by his new life, tried to escape it. After all as a man of God he was now spurned by him. He lashed out and killed a holy man, this gave him a new purpose. A goal in his unlife. He would kill those who did God's will in order to show mankind that nothing we do is right, that we can never truly understand our father above.
He meets another priest and tells him all of this. He means to kill this man but he doesn't react, at all. In fact he then tells the vampire that he is in fact God. That the vampire is just as stupid and blind as everyone he looks down on. He orders the vampire to walk into the dessert and wait for the sun to rise, he agrees and runs off to kill himself.
Moments later the sheriff shows up and we learn that this man isn't God, he isn't even a priest. He is just a crazy person off of his meds. It is such a great story that pulls you in and makes you think. It shows you how powerful faith is but also how dangerous it can be in the wrong hands. This story is an extremely important one, not just as a Buffyverse story but as a story about faith and humanity.