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The Institutio Generalis Missalis Romani is the document which instructs the pastors and the faithful on the correct way to celebrate the Eucharist. In its paragraph 53, it mentions the Gloria:
The Gloria
The Gloria is a very ancient and venerable hymn in which the Church, gathered together in the Holy Spirit, glorifies and entreats God the Father and the Lamb. The text of this hymn may not be replaced by any other text. The Gloria is intoned by the priest or, if appropriate, by a cantor or by the choir; but it is sung either by everyone together, or by the people alternately with the choir, or by the choir alone. If not sung, it is to be recited either by all together or by two parts of the congregation responding one to the other.
It is sung or said on Sundays outside the Seasons of Advent and Lent, on solemnities and feasts, and at special celebrations of a more solemn character.
Therefore, the Sacred Congregation for Divine Worship and Discipline of the Sacraments, which edited this text, makes it explicit here that it is a hymn of glorification and entreating the Father and the Son. This identity as a hymn of primarily praise also explains why it is omitted in Advent and Lent, which are more penitential seasons. Finally, the "proper" name for the Gloria, Major Doxology, points to it being a hymn of saying (λογία logia) glory (δόξα doxa) to God.