O Pastor Ecclesiae, tu omnes Christi pascis agnos et oves
O Shepard of the Church, you feed all Christ's lambs and sheep
The Feast of the Chair of Saint Peter celebrates the role and office of Saint Peter within the Church, the Mystical Body of Christ. It celebrates what the chair stands for - the role as shepherd and Bishop of the universal Church and the unity that the Chair symbolizes. This authority comes from Matthew 16:18 -
18 And I say to thee: That thou art Peter; and upon this rock I will build my church, and the gates of hell shall not prevail against it.
In his encyclical Satis Cognitum, Pope Leo XIII wrote:
[I]t is clear that by the will and command of God the Church rests upon St. Peter, just as a building rests on its foundation. Now the proper nature of a foundation is to be a principle of cohesion for the various parts of the building. It must be the necessary condition of stability and strength. Remove it and the whole building falls. It is consequently the office of St. Peter to support the Church, and to guard it in all its strength and indestructible unity.
And in the words of Saint Pope John Paul II,
On the feast of the Chair of St Peter, the liturgy once again offers us the famous oracle of the prophet Ezekiel, in which God reveals himself as the Shepherd of his people. Indeed, the chair is inseparable from the pastoral staff, because Christ, Teacher and Lord, came to us as the Good Shepherd (cf. Jn 10: 1-18)
Finally, in an excerpt from The See of Saint Peter, by Jacques Bossuet:
"It was, then, clearly the design of Jesus Christ to put first in one alone, what afterwards He meant to put in several; but the sequence does not reverse the beginning, nor the first lose his place. That first word, Whatsoever you shall bind, said to one alone, has already ranged under his power each one of those to whom shall be said, Whatsoever you shall remit; for the promises of Jesus Christ, as well as His gift, are without repentance; and what is once given indefinitely and universally is irrevocable. Besides, that power given to several carries its restriction in its division, while power given to one alone, and over all, and without exception, carries with it plenitude, and, not having to be divided with any other, it has no bounds save those which its terms convey."
Pope Francis, in the sensus fidelium, writes that he views the role in the Chair of Saint Peter as the coordinator and animator of the faith, that the role is not to flaunt his role of authority but rather to serve the Church through it's leadership through guidance from the Holy Spirit. Though often separated from each other by great distances, the early churches founded by the Apostles remained connected in faith under the leadership of Saint Peter. The feast celebrates this unity that Christ created for his church.
At least two feasts were celebrated in the early church - January 18th with his stay in Rome and February 22 with his stay in Antioch. Both feasts were included in the Tridentine Calendar and raised to Greater Doubles in 1604 by Pope Clement VIII. In 1960, Pope John XXIII removed the January 18th feast and moved the February 22nd Feast to a Second-Class Feast. The 1969 Revision lists the Feast of the Chair of Saint Peter on February 22nd with the rank of Feast.