"Flesh and blood has not revealed this to you, but my heavenly Father" (Matt 16:16).
Jesus chooses Peter to lead the Apostles because he sees that his Abba has already chosen to reveal to him what no human insight could grasp. Peter somehow perceives that this man Jesus standing in front of him is in fact the promised messiah, the anointed one and, even more, the "Son of the living God."
At this crucial turning point in his ministry, by all accounts at the peak of his power and popularity, Jesus knows that his messianic call will be fulfilled not in some imagined victory over his enemies and against all resistance, but in submitting to apparent defeat, rejection and death. His quizzing of his disciples is crucial before they all turn south to Jerusalem.
Peter gets half the message. He affirms that Jesus is the one they have been waiting for, but he rejects the path of suffering and death Jesus reveals. He does not understand the paradox of a messiah who completes his mission by becoming the suffering servant. Jesus' praise turns to a sharp rebuke. All of the disciples have yet to learn that they, too, will have to go through a transformation to share in the paschal mystery of glory through suffering.
We want to be successful, to fulfill our lives and accomplish God's will. God gives us insight and courage each step of the way. But if we are serious about following Jesus and imitating the pattern of his downward path through compassion and self-sacrifice, we must pray for the call within the call, the grace within the grace, that will lead us through the difficult losses every vocation faces. We pray to find the fullness that can only happen if we are willing to come in on empty -- of ourselves and our own agendas.