The Sacred Liturgy Nos. 9 & 10

9. The Gloria…
The Gloria is an ancient and venerable hymn to the Trinity. The Church, gathered by the Holy Spirit, sings her praises to the Father and the Lamb, Jesus Christ. Its opening phrases are taken from the proclamation of the angels at the birth of Jesus: “Glory to God in the highest, and on earth peace to people of good will!” (Luke 2:14)
This hymn follows the Act of Penitence, on Sundays outside Lent and Advent, and on Solemnities and Feasts of the Church calendar, including some celebrations of the Blessed Virgin Mary and the Saints. When the Gloria is proper to the Mass of the day, it must be sung, or at least recited, and may never be replaced by any other text. It is customary in many places to ring the church bells during the Gloria on Christmas, Holy Thursday, and at the Easter Vigil.
This hymn of the angels constantly reminds us of Christmas. We recall as we participate in the celebration of Mass, that Jesus comes among us in the Eucharist as really and substantially as He did when He was born as a man.
GIRM 53

10. The Collect
In the Mass, the Gloria is followed by the Collect. The Collect, the Prayer over the Gifts (Super Oblata), and the Postcommunion Prayer, are the three principal prayers unique to the Mass of each day. They relate to the Liturgical Season or to the celebration of an event in the life of Jesus, Mary, or the Saints. The Collect expresses the “theme” of the celebration. Listening to it allows one to absorb the meaning of the Mass of the day.
After the Gloria, the priest invites the people to pray, saying “Let us Pray.” All observe a brief period of silence in order to be recollected in God’s presence and to bring to mind each one’s individual prayers. The priest prays the Collect, gathering together the prayers of the people, and offering the official prayer of the Church. The Collect is a prayer addressed to the Trinity: to God the Father, through Jesus Christ, in the Holy Spirit.
The words of the Collect, as with all liturgical prayers, are written by the Church in a particular way and connect to certain events in the Liturgical Cycle. They cannot be changed or replaced according to anyone’s personal desire.
GIRM 54