Gates are there to keep people “in” and I would add that gates are also there to keep enemies “out.” The answer is right there in the Creed: “mortuus, et sepultus, descendit ad inferos, tertia die resurrexit a mortuis …” that is “He died and was buried, He descended into Hell on the third day He rose again from the dead …” The victory of Jesus is “coming in and coming out” of Hades as He pleases, like a true conqueror. But I think there is much more to those gates.
Before Jesus gives this short discourse to the twelve He takes them to Caesarea. As the name of the region indicates that is the part of Judea reserved to the Romans, Greeks and other non-Jews. Just like the Decapolis where Jesus found the poor man possessed by a legion of demons, that was an area where only a renegade Jew would reside. There is, I believe, a purpose to choose that odd location. The Romans were in control of the citadel in Jerusalem, that was the ancient residence of the Jewish kings from the days of David. There the Romans had done something quite offensive: they forced the High Priest, Annas, to resign and to take part on a rotational High Priesthood assignment along with all the males in his family. St John tell us that year the turn for the High Priesthood would fall on Caiaphas (pron. kaea-fash) who was Annas’ son in law. For the Romans there could be only one life-long high priest and that was the Emperor, Tiberius. No competition was allowed. The spurious high priesthood of Caiaphas was one of the reasons why the trial of Jesus was an invalid farce.
Keep that in mind as we see how Jesus brings his own judgment on Caesar and the Romans. First he responds to the geographic challenge by taking the twelve to the Roman reserve. The twelve here represent the twelve tribes of the new Israel Jesus is about to launch into the world as the beginning of the new creation: “Look! I am making all things new.” So he takes his royal court to a place, a small valley where the Romans had a cave dedicated to Pan who was the ruler of the underworld, the human passions, etc. I read somewhere that the cave was enclosed by iron gates to preserve the offerings of food and other valuables inside. Those were known as the gates of Hell, at the time containing the bulk of the human race in one way or another. Remember the previous words of Jesus: “But no one can enter the strong man’s house and plunder his property unless he first binds the strong man first.” Jesus is about to begin the conquest of the world by tying the strong man, sin that keeps mankind within the gates of Hell.
So he asks the disciples about who people do think He is, then who do they think He is. Peter responds and here the plot thickens! Peter is given a new name, indicative of a new important mission. His name is Kepha, which is phonetically very similar to Caiaphas but it is also its opposite: Kepha (a rocky promontory) ~ Caiaphas (a dell, or depression, a small valley.) Then the Lord uses the words of Isaiah 22: 22 when God replaces the vizier of the royal house of Israel (a post instituted by king Solomon) with a better man whom God promises to establish firmly like a wooden peg on the rock-mass.
In time Kepha Peter will go to Rome and die a sacrificial death on the Mons Vaticanus, the hill where the ancient “augures” would give their “vaticinii” or prophecies learned from reading the entrails of a doe, “venter.” That hill where later the Romans installed their Circus, contained a mysterious “gate to Heaven” through which Peter went the day he was crucified upside down. Think of the image: Peter’s crucifixion “reflects” Christ’s crucifixion as if the world was a mirror of Heaven, something that reminds me of the “aleph” the first letter of the Hebrew alphabet, a sort of ideogram resembling a tiny man pointing his right hand to Heaven and his left pointing to Earth.
In time the successors of Peter would conquer Rome. The basilicas were used for Christian temples; the purple of the emperors turned into the purple of the bishops; the paternity of the Emperor ceded the way to the paternity of the Roman Pontiff; and in a curious twist Jesus –in true Oriental monarch fashion– appropriates the “tongue” of the Emperor and makes it the language of the Church. That is reminiscent of the ancient oriental custom of cutting the tongue of the conquered king to prevent him to address his troops ever again.
Christ conquered Rome with the Church because, as C. S. Lewis noticed, the enemy of God preaches that sovereignty is not the result of creation but of conquest. So now Jesus turns the enemy’s logic on itself: God will own the world because He is the Creator, and also because He has conquered it.