Why a Pope ?
Jesus had chosen Peter as his church’s chief. Jesus knew that Christianity would become hierarchical. Peter had a heart so turned to Christ that Jesus pointed him out.
Thus there have been popes who have succeeded each other since Peter, first in a hidden way, then in Rome when Constantine designated Christianity as the Roman religion.
Thus the Vatican in Rome is the place where the various popes who succeeded each other resided. The Pope is in the Vatican.
Search the popes’ chronology.