Today, Februrary 22, is the Feast of the Chair of St. Peter the Apostle. This chair is the key to the unity of all Christians, as I explained here. That is in part because it not just a chair, but a throne (θρόνος), or cathedra, i.e. a seat of authority. God promised that Jesus would be given the throne of His father David.
"He will be great and will be called the Son of the Most High; and the Lord God will give Him the throne of His father David." (Luke 1:32)
Jesus instructed His Apostles to explain that the Kingdom (i.e. the Church) was here.
"And as you go, preach, saying, 'The kingdom of heaven is at hand.'" (Matthew 10:7)
Jesus promised the Apostles that in His Kingdom (i.e. Church), they would sit on thrones and judge the new Israel.
"As My Father appointed a kingdom for Me, so do I appoint for you that you may eat and drink at My table in My kingdom, and sit on thrones judging the twelve tribes of Israel. Simon, Simon, behold Satan demanded to have you, that he might sift you like wheat, but I have prayed for you that your faith may not fail; and when you have turned again, strengthen your brethren." (Luke 22:29-32)
God had promised to David that his son would sit on his throne, and build the house of His name.
"Your son, whom I will set on your throne in your place, he will build the house for My name." (1 Kings 5:5)
But Solomon was a type of Christ, for Christ is building the Church, which is the temple of God. God had promised to David that his throne would be established forever, and that he would not lack a man on his throne.
"then I will establish the throne of your kingdom over Israel forever, just as I promised to your father David, saying, 'You shall not lack a man on the throne of Israel.'" (1 Kings 9:5)
This promise was fulfilled when Christ the King, the Son of David, conceived by the Holy Spirit, established the Kingdom that will never end.
"As you looked, a stone was cut out by no human hand, and it struck the image on its feet of iron and clay, and broke them in pieces ... But the stone that struck the image became a great mountain and filled the whole earth. ... And in the days of those kings the God of heaven will set up a kingdom which shall never be destroyed, nor shall its sovereignty be left to another people. It shall break in pieces all these kingdoms and bring them to an end, and it shall stand forever." (Daniel 2:34,35,44)
This kingdom will continue to increase, will never be overturned, because it is divinely established.
"Of the increase of His government and of peace there will be no end, upon the throne of David, and over his kingdom, to establish it and to uphold it with justice and righteousness from this time forth and forevermore." (Isaiah 9:7)
Christ, the Chief Cornerstone, designed Peter the rock, upon whom to build His Church. This is the Kingdom that will never be defeated, but will prevail to the end.
"And I say to you that you are Peter, and upon this rock I will build My Church; and the gates of Hades will not prevail against it. I will give to you the keys of the kingdom of heaven, and whatever you bind on earth shall be bound in heaven, and whatever you loose on earth shall be loosed in heaven." (Matthew 16:18-19)
Christ has given stewardship of His Kingdom to His steward. This is the Petrine office, the chair of St. Peter the Apostle.
"Who then is the faithful and sensible steward, whom his master will put in charge of his servants, to give them their rations at the proper time?" (Luke 12:42)
Christ rules the Church through the men He has entrusted with the keys of His Kingdom, and given them authority to speak in His name.
"The one who listens to you listens to Me, and the one who rejects you rejects Me; and he who rejects Me rejects the One who sent Me." (Luke 10:16)
In the discussion of the sacrament of Holy Orders in the Supplement of St. Thomas Aquinas's Summa Theologica, we find the following question: Whether in the Church there can be anyone above the bishops? (Supp. Q.40 a.6) The answer given is as follows:
We read in the council of Constantinople [381 AD]: "In accordance with the Scriptures and the statutes and definitions of the canons, we venerate the most holy bishop of ancient Rome the first and greatest of bishops, and after him the bishop of Constantinople." Therefore one bishop is above another.
Further, the blessed Cyril, bishop of Alexandria (375-444 AD), says: "That we may remain members of our apostolic head, the throne of the Roman Pontiffs, of whom it is our duty to seek what we are to believe and what we are to hold, venerating him, beseeching him above others; for his it is to reprove, to correct, to appoint, to loose, and to bind in place of Him Who set up that very throne, and Who gave the fullness of His own to no other, but to him alone, to whom by divine right all bow the head, and the primates of the world are obedient as to our Lord Jesus Christ Himself." Therefore bishops are subject to someone even by divine right.
... Wherever there are several authorities directed to one purpose, there must needs be one universal authority over the particular authorities, because in all virtues and acts the order is according to the order of their ends (Ethic. i, 1,2). Now the common good is more Godlike than the particular good. Wherefore above the governing power which aims at a particular good there must be a universal governing power in respect of the common good, otherwise there would be no cohesion towards the one object. Hence since the whole Church is one body, it behooves, if this oneness is to be preserved, that there be a governing power in respect of the whole Church, above the episcopal power whereby each particular Church is governed, and this is the power of the Pope. Consequently those who deny this power are called schismatics as causing a division in the unity of the Church. Again, between a simple bishop and the Pope there are other degrees of rank corresponding to the degrees of union, in respect of which one congregation or community includes another; thus the community of a province includes the community of a city, and the community of a kingdom includes the community of one province, and the community of the whole world includes the community of one kingdom.
... Although the power of binding and loosing was given to all the apostles in common, nevertheless in order to indicate some order in this power, it was given first of all to Peter alone, to show that this power must come down from him to the others. For this reason He said to him in the singular: "Confirm thy brethren" (Luke 22:32), and: "Feed My sheep" (John 21:17), i.e. according to Chrysostom [347–407 AD, Archbishop of Constantinople]: "Be thou the president and head of thy brethren in My stead, that they, putting thee in My place, may preach and confirm thee throughout the world whilst thou sittest on thy throne."
The chair of St. Peter stands in St. Peter's Basilica in Rome, over the bones of St. Peter: (H/T: The Adoption Report)
Father in heaven, please bless and strengthen the episcopal successor of St. Peter, through whom you have provided the way to the unity of all your people, throughout the world, in the one, holy, catholic and apostolic Church. Please help all your people see and embrace this gift you have provided to the Church, that in her unity she may show to the world the most perfect unity and love within your holy and eternal communion of divine Persons. In the name of the Father, and of the Son, and of the Holy Spirit. Amen.
UPDATE: Today, Pope Benedict said:
"This Sunday is also the feast of the Chair of Peter, an important liturgical feast that highlights the office of the successor of the Prince of the Apostles. The chair of Peter symbolizes the authority of the Bishop of Rome, who is called to perform a special service for the whole People of God. Immediately after the martyrdom of St. Peter and St. Paul, the primacy of the Church of Rome in the Catholic community was recognized. This role was already attested to in the 2nd century by St. Ignatius of Antioch (Letter to the Romans, Pref.: Funk, I, 252) and by St. Irenaeus of Lyons (Contra Haereses, III, 3, 2-3). This singular and specific ministry of the Bishop of Rome was stressed again by the Second Vatican Council. "Moreover, within the Church," we read in the Dogmatic Constitution on the Church, "particular Churches hold a rightful place; these Churches retain their own traditions, without in any way opposing the primacy of the Chair of Peter, which presides over the whole assembly of charity (cf. St. Ignatius of Antioch, Letter to the Romans, Pref.) and protects legitimate differences, while at the same time assuring that such differences do not hinder unity but rather contribute toward it" (Lumen Gentium, 13).