Is Jesus our king? Did He re-establish the office of the Royal Steward?
In ancient times, a king might choose a second in command (known as the royal steward or prime minister) who literally wore a large key as a symbol of his office and who spoke with the authority of the king. The prophet Isaiah confirms this:
"In that day I will summon my servant, Eliakim son of Hilkiah. I will clothe him with your robe and fasten your sash around him and hand your authority over to him. He will be a father to those who live in Jerusalem and to the house of Judah. I will place on his shoulder the key to the house of David; what he opens no one can shut, and what he shuts no one can open.”
In the passage above, God is speaking, and He confirms the existence of the office, the key, and the continuation of the office despite the change of office holder. In other words, the office of the royal steward continued even when the man who held the office died or was replaced by someone else. God Himself passes the key from one steward to the next.
In the New Testament, we learn that Jesus inherits the throne of his father, David.
And behold, you will conceive in your womb and bear a son, and you shall call his name Jesus. He will be great, and will be called Son of the Most High; and the Lord God will give to him the throne of his father David, and he will reign over the house of Jacob forever; and of his kingdom there will be no end.
We also read the following:
When Jesus came to the region of Caesarea Philippi, he asked his disciples, “Who do people say the Son of Man is?” They replied, “Some say John the Baptist; others say Elijah; and still others, Jeremiah or one of the prophets.” “But what about you?” he asked. “Who do you say I am?” Simon Peter answered, “You are the Christ, the Son of the living God.” Jesus replied, "Blessed are you, Simon son of Jonah, for this was not revealed to you by man, but by my Father in heaven. And I tell you that you are Peter, and on this rock I will build my church, and the gates of Hades will not overcome it. I will give you the keys of the kingdom of heaven; whatever you bind on earth will be bound in heaven, and whatever you loose on earth will be loosed in heaven.
The passage quoted above from Matthew tells us that Jesus named Peter as His royal steward and gave him the “keys to the kingdom of heaven" as the symbol of his authority to speak in His name. Since Jesus is an eternal king, the office of royal steward in His kingdom will never end. Peter died as a martyr as Jesus foretold, but the successors of Peter have taken his place in the perpetual office that Jesus established in His royal court.
In addition to the reference to a key or keys, note the following parallels:
"What he opens no one can shut, and what he shuts no one can open.” (Is. 22:22)
"Whatever you bind on earth will be bound in heaven, and whatever you loose on earth will be loosed in heaven.” (Mt. 16:19)
Jesus specifically referenced the passage from Isaiah when He appointed Peter, and Peter received authority from Jesus to speak universally in His name. To do so faithfully, Peter must not teach error; therefore, Peter (and his successors who hold the office of the Royal Steward - also known as the Bishop of Rome) are protected by God through the charism of infallibility.