From: The Angels. The Catholic Teaching on the Angels, by Fr. Pascal P. Parente. pg. 31, from the section “The Language of Angels”
At the birth of Christ, the heavenly messenger of joy and of great tidings, an Angel of God announced the nativity of the Savior of the world to a few shepherds in the hill country around Bethlehem. Messengers had come down to earth many times since man’s creation, to advise, to warn, to help, or to punish man. On this occasion “a multitude of the heavenly army” was heard for the first time singing, caroling, and praising God and saying: “Glory to God in the highest, and on earth peace to men of good will.” Only the Angelic mind could well understand the mystery of the Incarnation, and the great honor and dignity that had come to poor human nature when the Son of God, the Eternal Word, assumed and substantially united it to His Divine Person for all eternity.
And I just had to add this one, in light of some recent discouragements: