No Gloria during Advent?

During Advent, we refrain from singing the “Gloria in Excelsis Deo / Glory to God in the Highest.” Why?
Let’s start with some basic rules of liturgy set down by the Second Vatican Council in its Constitution on the Sacred Liturgy. Within the cycle of a year the Church “unfolds” the whole mystery of Christ, from the incarnation and birth until the ascension, the day of Pentecost, and the expectation of blessed hope and of the coming of the Lord (no.102). The church is to be particularly directed toward feasts of the Lord that point to salvation (no.108).

In other words, a principle in ritual is to celebrates “feasts” and “fasts” in different ways so as to allow the mysteries of Christ to be made clear by the celebration. The Resurrection of Christ takes pre-eminence and is characterized by 40 days of Lenten penance followed by the Sacred Triduum and 8 full days (the “Octave”) of Easter. In the same way, Advent precedes Christmas as a time of preparation. In a sense, we “fast” in the liturgy to prepare for the “feast” of Christmas! Finally, we remember again where the first words of the Gloria came from: the Angels sang it to the shepherds the very night that Jesus was born! So when we sing the Gloria at Midnight Mass, we are caught up in a tremendous “feast” of Christmas joy!