Jesus was referring to Isaiah 22:16-22: ‘Thus says the Lord, the GOD of hosts: Up, go to that official, Shebna, master of the palace, Who has hewn for himself a sepulcher on a height and carved his tomb in the rock: “What are you doing here, and what people have you here, that here you have hewn for yourself a tomb?” The LORD shall hurl you down headlong, mortal man! He shall grip you firmly And roll you up and toss you like a ball into an open land To perish there, you and the chariots you glory in, you disgrace to your master’s house! I will thrust you from your office and pull you down from your station. On that day I will summon my servant Eliakim, son of Hilkiah; I will clothe him with your robe, and gird him with your sash, and give over to him your authority. He shall be a father to the inhabitants of Jerusalem, and to the house of Judah. I will place the key of the House of David on his shoulder; when he opens, no one shall shut, when he shuts, no one shall open.’
The House of David is the Reign of David, the lineage tracing back to King David which is required of the Messiah. It would seem, at first glance, that Jesus is calling Peter the Messiah, but this would be contrary to his earlier confession of who Jesus is. On second glance, and in light of the Tradition of the Church and of the analogy of faith, Jesus is calling Peter the Vicar of Christ.
Allow me to expand on what I mean.
In the Scriptures, there is only one instance of the word “vicar”, and it is in 2 Kings 23:4: ‘Then the king commanded the high priest Hilkiah, his vicar, and the doorkeepers to remove from the temple of the LORD all the objects that had been made for Baal, Asherah, and the whole host of heaven. He had these burned outside Jerusalem on the slopes of the Kidron and their ashes carried to Bethel.’
Now, a scholar might ask, “If the priest is the vicar of the king, than how can the Pope be the Vicar of Christ? Or how can Peter be the Vicar of Christ if he was not a priest?”
To answer the second question:
Jesus clearly gives the Apostles a share in His priestly office when, in John 20:21-23, He says: ‘(Jesus) said to them again, “Peace be with you. As the Father has sent me, so I send you.” And when he had said this, he breathed on them and said to them, “Receive the Holy Spirit. Whose sins you forgive are forgiven them, and whose sins you retain are retained.”’
The Father sent Jesus as High Priest and as Lamb of God to offer Himself in atonement for the sins of mankind; therefore, Jesus is sending the Apostles as priests: He is giving them the office of the priesthood. Peter was especially given the priesthood, as Jesus says: “Whose sins you forgive are forgiven them, and whose sins you retain are retained.” Only the High Priest in Judaism could ask God to forgive people their sins. Jesus is speaking to all His Apostles, but He is singling out Peter, the leader of the Twelve. (Since there is only Lamb of God, the Apostles were not made lambs; but since they are members of Christ’s Flock, they are called sheep. Just as Jesus was High Priest and Lamb of God, so too are the Apostles both shephards and sheep.)
Hence, Peter was truly given the office of Vicar of Christ. The papal title ‘Vicar of Christ’ is clearly biblical than. But that is not all! There is one more verse I want to bring to attention:
In John 21:15-17, we read: ‘When they had finished breakfast, Jesus said to Simon Peter, “Simon, son of John, do you love me more than these?” He said to him, “Yes, Lord, you know that I love you.” He said to him, “Feed my lambs.” He then said to him a second time, “Simon, son of John, do you love me?” He said to him, “Yes, Lord, you know that I love you.” He said to him, “Tend my sheep.” He said to him the third time, “Simon, son of John, do you love me?” Peter was distressed that he had said to him a third time, “Do you love me?” and he said to him, “Lord, you know everything; you know that I love you.” (Jesus) said to him, “Feed my sheep.”’
In those days, the shephard was the one who fed his sheep and took care of them. Hence, Jesus is making Peter the shephard of His flock.
In the Catholic Church, all of the bishops are shephards of their particular flocks, but only the Pope is the Shephard of the entire Flock of Christ.
To answer the first question:
Finally, the office of Pope is a priestly office. Any man may become Pope, but if he is not yet a bishop, he must first be given the office of Bishop, and than he is given the office of Pope. (The bishops are the successors of the Apostles, and are spoken of in Titus 1:7-9: ‘For a bishop as God’s steward must be blameless, not arrogant, not irritable, not a drunkard, not aggressive, not greedy for sordid gain, but hospitable, a lover of goodness, temperate, just, holy, and self-controlled, holding fast to the true message as taught so that he will be able both to exhort with sound doctrine and to refute opponents.’)