On This Rock

"You are Rock and on this rock I will build my church," declares Jesus to Peter in Matthew 16:18.  Before this incident "rock" was never used by anyone as a name.  Jesus is affirming Simon's leadership by giving him a title.  By the time Matthew's Gospel was written Peter would have moved to Rome and would have been martyred there.  Though  there is nothing in the New Testament to indicate that Peter's leadership was passed on to a successor, it is significant that 15-20 years after his martyrdom Matthew and his community remember and record these words of Jesus.
Peter would not have been bishop of Rome in the way that we understand "bishop," but he may well have been the leader of one of the several Christian communities in that city.  Because Rome was the center of the Empire as well as the city where Peter and Paul had been martyred, the leader of the church there gradually over the next few centuries became acknowledged as leader by Christians in other places.
It is because he is bishop of Rome that the Pope is the leader of the Church.  By retiring from the office of bishop of Rome, Benedict helped us to see that the papacy was an office, not a personal privilege.  Pope Francis underlined this understanding of the position in the brief speech he made on the evening of his election.   He began, "You all know that the duty of the Conclave was to give a bishop to Rome."  Four times he referred to himself as bishop, never using the title "pope."  He even referred to his predecessor as "Bishop Emeritus Benedict XVI."  Many of us took this to mean that Francis intended to treat other bishops with the respect that is owed them as successors of the Apostles.