Jesus asks his question in a strange place. Caesarea Philippi was built around a cliff face devoted to the worship of Pan, in the shadow of a temple honoring Caesar's own divinity. Every rival claim to godhood in that world had a shrine near this spot. It is here, surrounded by other men's gods, that he asks the question this Gospel has been circling since its first chapter. 15"But who do you say that I am?"
The disciples' first answers come easily, and all of them are secondhand: John the Baptist, Elijah, Jeremiah, one of the prophets. Each answer is respectable, and none is true. Then Jesus makes it personal, and Peter gives the fullest confession anyone in the Gospel has spoken: 16"You are the Christ, the Son of the living God."
Jesus tells Peter where the confession came from. 17"Flesh and blood has not revealed this to you, but my Father who is in heaven." The Father showed a fisherman what none of Jesus' sharpest critics, watching the same miracles, ever managed to see. This is revelation, plain and simple, and whatever else we say about Peter in the rest of the story, this sentence was never his own achievement to take credit for.
18"You are Peter, and on this rock I will build my church." Whole libraries have been written on what the rock is, Peter himself, the confession he just made, or Christ, whom Peter points to. Most readings agree on one thing. Whatever authority Peter is given here is never separate from what he just said. The building rests on Christ, who is doing the building. Gates are built to defend, so the promise that the gates of hell will not prevail pictures the church advancing on death's own fortress and finding the gates unable to hold. It does not depend on the strength of those doing the confessing.
Then come 19"the keys of the kingdom of heaven." Two chapters later the same authority to bind and loose is given to the whole community of disciples (Matthew 18:18). It is authority exercised in step with what heaven has already decided, the church on earth announcing and enacting what the Father has decreed, opening the door to everyone who makes Peter's confession.
Immediately, having reached the highest point any human being in this Gospel has climbed, Jesus tells them to say nothing yet. The confession is true, but its full meaning, a Messiah who must suffer and die before he reigns, has not been given to anyone in that circle to carry safely. Just a few verses later Peter will hear the difference. When he objects to the cross, Jesus turns and says, 23"Get behind me, Satan!" The man who spoke the truth by revelation is the same man who resists it when it costs something.
Your clearest confessions of Christ were never your own achievement either. Rest in that. Then keep confessing what you have been given, even in the years before you understand everything it will cost.
Prayer
Father, we confess with Peter that Jesus is the Christ, the Son of the living God, and we know as surely as he did that no flesh and blood taught us to say it. Thank you for building your church on Christ and on a confession instead of on our own strength. Keep us confessing the truth even before we understand what it will cost us. In Jesus' name, amen.