More things I didn't know about the traditional Roman Rite liturgy. . .

. . .again from the Blessed Cardinal Schuster's Liber Sacramentorum, this time discussing the Fourth Sunday after Pentecost:

The progressive order of the psalms for the Introit shows us that these Masses of the Sundays after Pentecost formed "originally a series by themselves, which now, unfortunately, has been disturbed by frequent breaks, which date from the seventh century at least. The Würzburg list of Gospels indicates that there were at Rome in the eighth century two "Second Sundays" post Pentecosten, one ante natale Apostolorum and the other post natale Apostolorum; after which the cycle continued with the dominica tertia, and so on. It is important to note that the Feast of SS Peter and Paul, like the other greater solemnities of the year, formed a chronological milestone from which the various weeks of the liturgical year were reckoned. To-day's Gospel of the miraculous draught of fishes taken by St Peter is assigned in the same list to the second Sunday (ante natale Apostolorum), and refers, perhaps, to the feast which Rome was already beginning to celebrate with still greater solemnity. We can hardly picture to ourselves in these times the devotion with which the natalis of the Apostles Peter and Paul was celebrated at Rome in the early days of Christianity. From all over Italy, even from the most remote provinces of the empire, bands of pilgrims arrived for this occasion, to whom Rome was the type of the heavenly Jerusalem, the city of the martyrs.

The Introit is drawn from Psalm xxvi, and well reflects the mind of the Church during this period of combat and peril: "The Lord is my light and my salvation; whom shall I fear? The Lord is the protector of my life; of whom shall I be afraid? My enemies that trouble me have themselves been weakened and have fallen." This miracle, described by the Evangelists as having taken place when Jesus was made captive in the Garden of Gethsemani, is constantly being renewed in the history of the Church, wherein we find that all those who have made war upon her have always ended in disaster and ruin.

The melody of this psalm must have had a special pathos when sung by the terrified band of faithful Christians in the darkness of the catacombs. "The Lord is my light and my salvation; whom then shall I fear?" Nero, Domitian, and Valerian have each been cast down from his throne by the hand of God. That Church which they sought to destroy stands still unmoved, and the morrow draws near when, from the height of the Vatican, she shall rule in the place of the Caesars over all the nations of the world.

The Collect appears to pursue the same thought, as is seen in the Introit. Of very great importance to the expansion of the Church are the social conditions of a country. These are subjected to God in such a way that, whilst the nations are agitated and disturbed by their passions, he orders all these events and turns them to his final glory and to the salvation of souls. We therefore join to-day in the Church's prayers that the divine Providence may so dispose the course of human affairs that nothing shall arise to hinder the Catholic family from giving to God the united homage of its devotion. In other words, we beseech almighty God not to permit the return of persecution, because, although it might enrich the Church with martyrs, yet the normal life of the Christian community develops more freely during times of peace and goodwill.