The Church keeps a solemn feast of the chair of Saint Peter, to wit, when he is said to have been raised up to the honor of the chair (or ‘a throne’) at Antioch. And some people say that this raising up was done by Theophilus, the prince of Antioch, whose deceased son Peter raised up after 14 years. (This would be the same Theophilus to whom St Luke addresses his Gospel and the Acts.) And he converted the people of the city, for which reason they built a church there, and set a high throne up in the midst of it, so that Peter could be heard and seen by all, and he sat upon it for seven years. Therefore the Church keeps a solemn feast in regard to this honor, because then did its prelates begin to have the first place and be honored, and the words of the Psalmist (106, 32) were fulfilled, “Let them exalt him in the church.”
In the following video, the Gradual of the feast of St Peter’s Chair is sung as part of the common Mass of Holy Popes, beginning at 19:50. The recording was made on the feast of Pope St Clement I in 2019.
Graduale, Ps. 106 Exaltent eum in Ecclesia plebis, et in cáthedra seniórum laudent eum. V. Confiteantur Dómino misericordiae ejus, et mirabilia eius filiis hóminum. (Let them exalt him in the assembly of the people, and praise him upon the seat of the elders. V. Let the mercies of the Lord give Him thanks, and His wondrous deeds confess Him to the children of men.)
And note that he is exalted in three ways, and therefore a threefold feast is celebrated. First, he is exalted in the Church militant, presiding over it and ruling over it laudably, in faith and morals… Secondly, in the Church of those who work malice *, namely by scattering it, and converting it to the Faith; and to this belongs his second feast, that which is called the feast of the chains. Third, he is exalted in the Church triumphant, namely by happily entering into it, and to this belongs his third feast, that of his passion.
*This refers to an expression which occurs three times in the Psalms, “the council” (21, 17), “church” (‘ecclesia’, 25, 5), or “assembly (63, 3) of those who work malice (malignantium)”, here taken to mean those who need conversion.
He also has a threefold feast for five other reasons. First, because he was privileged above all others, and therefore he is honored above others in authority, since he was the Prince of the Apostles and received the keys of the kingdom of heaven. He was also more fervent in the love of Christ, and more effective in might, since at his shadow the sick were healed.
St Peter Healing the Sick with His Shadow, 1424-25, fresco by the Florentine painter Tommaso di Ser Giovanni di Simone (1401-28), commonly known as Masaccio; in the Brancacci chapel of Santa Maria del Carmine in Florence. (Public domainimage from Wikimedia Commons.)
Second, because of his office, since he had the office of authority over the whole Church, which is spread out unto the three parts of the world, namely, Asia, Africa and Europe, and therefore the Church keeps a solemn feast for him three times in the year.
Third, because of the good which he does, since he who has the power of binding and loosing delivers us from three kinds of sin, namely, of thought, word, and deed, and because we sin (in three ways), against God, against neighbor, and against ourselves.
This benefit can also be the threefold good which the sinner obtains in the Church by the power of the keys: the demonstration of his release from guilt, the commutation of the punishment of purgatory into a punishment in this world, and the relaxation in part of temporal punishment.
The fourth reason is because of what we owe him, since he has fed us and feeds us in three ways, by word, example, and temporal help.
The fifth is because of his personal example, so that no one may despair, even if he shall have denied Christ three times, as he did, as long as he wishes to confess God along with him, in heart, mouth, and deed. (William Durandus, Rat. Div. Off. 7, 8, 1-3)