"After the Act of Penitence, the Kyrie is always begun, unless it has already been included as part of the Act of Penitence. Since it is a chant by which the faithful acclaim the Lord and implore his mercy, it is ordinarily done by all, that is, by the people and with the choir or cantor having a part in it." (GIRM)
The Kyrie and the Gloria have been a part of the preparation to celebrate the Divine Mysteries of God since the very beginning. "The Kyrie [Lord have Mercy] is a remnant of those litanic dialogues, of those acclamatory prayers, which rose up spontaneously in the breast of the primitive Church. It originated in the Greek-speaking East, perhaps in Jerusalem where [it was heard] sung [in] about the year 500 [AD]. [The Kyrie] carries to the Three Divine Persons in turn, our heartfelt need and purposive desire for salvation." (This is the Mass (TM), 44)
The Kyrie and Gloria express two desires that arise in the hearts of man. "To give glory to God and to beg His mercy are the two purposes which link man to God: it is because we know that God is Almighty that we beseech Him to have mercy upon us." (TM, 44) In other words, we recognize that because God is glorious and worthy of praise (Gloria), we seek his forgiveness (Kyrie) before daring to enter into His dwelling place.
Immediately following the Kyrie, "there is intoned a hymn to the Majesty of God." (TM, 44) "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...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." (GIRM)
Historically speaking, the Gloria has been a part of the Church since the very beginning:
"The Gloria is a very old prayer, already in existence in the second century, which was incorporated into the Roman Mass in the sixth century. It opens appropriately with the words in which the angels sang praise 'to God in the highest;' for is not every Mass a renewal, in some sense, of Christmas, and does it not mark, once more, the Coming of Our Lord? " (TM, 44)
The words of the Gloria are rich in meaning, and start out with the words of the angels at the birth of Christ, "Glory to God in the Highest..." (see Luke 2:14) The remaining words were picked deliberately to help convey our own hearts thankfulness to God and our understanding of who He is. The deep meaning of the words can be seen especially in the recent translation of the Mass texts:
"In the [recent] translation [of the Mass], Jesus is addressed as the 'Only Begotten Son.' This more closely follows the theological language used in the early Church to highlight how Jesus is uniquely God's Son, sharing in the same divine nature as the Father. This also reflects the biblical language in John's gospel, which uses similar wording to describe Jesus' singular relationship with the Father." (A Guide to the New Translation of the Mass, 12)
As we progress through the Mass, let us remember that the Mass is ultimately a prayer of thanksgiving that gives honor and glory to God. Attending Mass gives us the opportunity to praise Him and recognize His presence in our lives. He is the Creator of the Universe and more importantly, the Creator of us! We owe everything to God and so it is "right and just" that we praise Him with every fiber of our being!
Glory to God in the highest,
and on earth peace to people of good will.
We praise you,
we bless you,
we adore you,
we glorify you,
we give you thanks for your great glory.
Lord God, heavenly King, O God, almighty Father.
Lord Jesus Christ, Only Begotten Son, Lord God, Lamb of God, Son of the Father,
you take away the sins of the world, have mercy on us;
you take away the sins of the world, receive our prayer;
you are seated at the right hand of the Father, have mercy on us.
For you alone are the Holy One, you alone are the Lord, you alone are the Most High, Jesus Christ, with the Holy Spirit, in the glory of God the Father, Amen.