When the pope celebrates divine service, as on Easter Sunday, Christmas Day, Whit Sunday, St. Peter and St. Paul, &c. the great or middle doors of the church are thrown open at ten, and […] [a] majestic procession is closed by the pontiff himself, seated in a chair of state, supported by twenty valets, half concealed in the drapery that falls in loose folds from the throne; he is crowned with his tiara […]  Towards the conclusion of these preparatory devotions his immediate attendants form a circle around him, clothe him in his pontifical robes, and place the tiara on his head […]He then proceeds in great pomp through the chancel and ascends the pontifical throne, while the choir sing the Introitus or psalm of entrance, the Kyrie Eleison and Gloria in excelsis, when the pontiff lays aside his tiara, and, after having saluted the congregation in the usual form, the Lord be with you, reads the collect in an elevated tone of voice. […]  The epistle is then read, first in Latin then in Greek; and after it some select verses from the psalms, intermingled with Alleluias, are sung to elevate the mind and prepare it for the gospel.

The pontiff then rises, gives his benediction to the two deacons that kneel at his feet with the book of the gospels, and resigning his tiara, stands while the gospel is sung in Latin and in Greek; after which he commences the Nicene Creed, which is continued in music by the choir. When the creed and the psalm that follows it are over, he descends from his throne […] He then turns to the people, and in an humble and affectionate address begs their prayers; and shortly after commences that sublime form of adoration and praise called the preface, because it is an introduction to the most solemn part of the liturgy, and he chaunts it in a tone supposed to be borrowed from the ancient tragic declamation, and very noble and impressive. The last words, "Holy, Holy, Holy, Lord God of armies," &c. are uttered in a posture of profound adoration, and sung by the choir in notes of deep and solemn intonation. All music then ceases, all sounds are hushed, and an awful silence reigns around.

[…]

 Shortly after the conclusion of this prayer, the pontiff salutes the people in the ancient form, "May the peace of the Lord be always with you," and returns to his throne, while the choir sing thrice the devout address to the Saviour, taken from the gospel, "Lamb of God who takest away the sins of the world, have mercy upon us."