From that time on, Jesus began to show his disciples that he must go to Jerusalem and suffer greatly from the elders, the chief priests, and the scribes, and be killed and on the third day be raised. Then Peter took Jesus aside and began to rebuke him, “God forbid, Lord! No such thing shall ever happen to you.” He turned and said to Peter, “Get behind me, Satan! You are an obstacle to me. You are thinking not as God does, but as human beings do.”
In today's Gospel, Jesus begins by asking his disciples who people think he really is. They respond with some of the speculations that were going round: he was John the Baptist resurrected from the dead or some of the great prophets. Then Jesus let them think for themselves, who He is for them. It was a moment of truth, a very special moment in his disciples' relationship with their Master.
Simon speaks up: "You are the Messiah, the Christ, the Son of the living God." It is a huge step forward for Peter and his companions. But it is not yet a total recognition of his identity or mission. He is praised for his insight but Jesus makes clear that it comes from divine inspiration. And then Jesus calls Simon "Peter", a play on the word for "rock". He is given the "keys of the kingdom", which is power and authority. We can see that his authority and that of the "church" is the authority of Jesus himself. Note that "Peter" in either its Aramaic or Hebrew was not a previously known personal name.
From the moment that they recognize Jesus as Messiah, He begins to prepare them for what is going to happen. "[The Son of Man] must go to Jerusalem to suffer greatly at the hands of the elders, the chief priests, and the scribes, and to be put to death, and raised up on the third day." It is hard for us to imagine the impact these words must have had. They just found out their Master was the Messiah, and Peter was just appointed as a leader, how could such terrible things happen? Peter takes Jesus aside and said: "God forbid, Lord! No such thing shall ever happen to you." He would never have thought that Jesus would call him Satan and an "obstacle". Not long ago, he is seen as a rock, and now he is seen as a stumbling block.
It will take time before Peter and the others both understand and accept the idea of a suffering and dying Messiah. We should also ask ourselves, to what extent we accept Jesus the rejected, suffering, dying and rising Messiah?