The Second Coming of Christ
"Ultimately, there is one set of keys and it is in the hand of the successor of St. Peter."
Actually there are more than one set of keys;
Rev 1:18 "I [am] he that liveth, and was dead; and, behold, I am alive for evermore, Amen; and have the keys of hell and of death."
Rev 3:7 "And to the angel of the church in Philadelphia write; These things saith he that is holy, he that is true, he that hath the key of David, he that openeth, and no man shutteth; and shutteth, and no man openeth;"
Rev 9:1 "And the fifth angel sounded, and I saw a star fall from heaven unto the earth: and to him was given the key of the bottomless pit. And he opened the bottomless pit; and there arose a smoke out of the pit, as the smoke of a great furnace; and the sun and the air were darkened by reason of the smoke of the pit."