This passage is among the most controversial in the Bible, as it is a focal point of debate between Roman Catholics, who reference it to argue that the passage makes Peter the leader of the original church (and thus the first pope) and those who oppose that idea. There’s actually something much more cosmic going on here. The location of the incident—Caesarea Philippi—and the reference to the “gates of hell” provide the context for the “rock” of which Jesus is speaking.
