The Angel announces that a King is born, and the choirs of angels unite their voice with his, and rejoicing all together they sing:
“Glory be to God in the highest, and on earth peace to men of good will.”
Before the Redeemer was born in the flesh, there was discord between us and the angels, from whose brightness and holy perfection we stood afar, in punishment first of original sin, and then because of our daily offenses. Because through sin we had become strangers to God, the angels as God’s subjects cut us off from their fellowship. But since we have now acknowledged our King, the angels receive us as fellow citizens.
Because the King of heaven has taken unto Himself the flesh of our earth, the angels from their heavenly heights no longer look down upon our infirmity. Now they are at peace with us, putting away the remembrance of the ancient discord ; now they honor us as friends, whom before they beheld weak and despised below them.
St. Gregory the Great, Homily 8 on the Gospels, 25 December 590
Locus Communis 