Christ comes to fulfil the prophecy that David’s throne would last forever. He holds the key of the Kingdom. Christ’s kingdom, however, is not of this world. He came and through His Passion He opened the gates of heaven that had been closed when Adam sinned.
Christ set about establishing heaven on earth. He called His apostles and said he was going to build a Church. As King He saw those who were to be His ministers in the Temple had reneged on their priestly duties. So, like King Hezekiah all those years a go, He dismissed the false stewards who had not cared properly for the kingdom and it’s people, and He gave the Key to a new Steward. He took Simon barJonah and gave him the Keys of the Kingdom. Jesus even used very similar words to King Hezekiah who placed the keys of his kingdom on the shoulder of Eliakim. “What you bind on earth is bound in heaven, what you loose on earth is loosed in heaven.” (Is.22:22 Matt 16:19)
Jesus takes the keys of the kingdom and passes His authority to the Church, His bride. Peter is the new Eliakim and he will pass on the keys to St. Linus, who into turn passes it on to St. ‘Cletus and then St. Clement and so on until Benedict XVI
Even as the little baby we will greet at Christmas there was an understanding that He is a king. It was the gentile Magi who brought Him the gifts for a king, gold for His kingship, frankincense for His priesthood and myrrh for prophecy.
From Lauds today:
The sceptre shall not pass from Judah, nor the mace from between his feet until the one comes to whom it belongs, to whole the people shall render obedience.
Gen 49:10. This is part of the blessing Jacob-Israel gave to his sons. Reuben had forfeited the blessing of the First Born because of the way he took revenge for the rape of his sister Dinah. Judah was the third born of Leah the first wife of Jacob-Israel.