When Peter was in Galatia and Paul sternly rebuked him for his hypocrisy.
Galatians 2:11-14, " But when Cephas came to Antioch, I opposed him to his face, because he had clearly done wrong. Until certain people came from James, he had been eating with the Gentiles. But when they arrived, he stopped doing this and separated himself because he was afraid of those who were pro-circumcision. And the rest of the Jews also joined with him in this hypocrisy, so that even Barnabas was led astray with them by their hypocrisy. But when I saw that they were not behaving consistently with the truth of the gospel, I said to Cephas in front of them all, “If you, although you are a Jew, live like a Gentile and not like a Jew, how can you try to force the Gentiles to live like Jews?”
Never forget what Jesus said to him: "But he turned and said to Peter, “Get behind me, Satan! You are a stumbling block to me, because you are not setting your mind on God’s interests, but on man’s.”
He never said anything close to that to any of the other apostles!
Peter was obviously a very conflicted, flawed man. He was the apostle to the Jews, but acted hypocritically, and Paul called him on it. Paul accused him of not behaving consistently with the truth of the gospel.
So, Jesus called him "Satan" and said he was a stumbling block (clearly contrasting with "on this rock I will build my church"). He accused him of setting his mind on man's interests, not God's.
Paul called him a hypocrite who didn't behave according to the gospel.
And this is the man who Catholics revere (in their own history) as the first Pope! Something is very definitely wrong here!!!