The Holy Mother of God.

"As the bush which Moses saw unconsumed, even so preserved is thy laudable virginity. O Mother of God, intercede for us!"
- Last antiphon, vespers of the feast.

A sermon by St. Leo the Pope:

Dearly beloved brethren, whosoever will keep this day's festival with true reverence and due honour, must neither think falsely of the Lord's Incarnation, nor meanly of the Godhead. For as there is danger of not realizing the truth of Christ's humanity, so is there no less danger of failing to recognize his equality in glory with his Father. Wherefore, when we try to contemplate the mystery of Christ's birth, wherein he was born of a Virgin Mother, we must soar above the clouds of earthly imagination, and with the eye of enlightened faith pierce through the fog of earthly wisdom.

The authority on which we believe is the authority of God himself ; and the teaching which we follow is the very teaching of God himself. Therefore it is true, whether we lend an ear to the testimony of the Law, or to the sayings of the Prophets, or to the trumpet of the Gospel. This latter did John the Son of Thunder sound, when, filled with the Holy Ghost, he proclaimed : In the beginning was the Word, and the Word was with God, and the Word was God ; the Same was in the beginning with God ; all things were made by him, and without him was not anything made. True also is the witness of John when he saith : The Word was made flesh, and dwelt among us, and we beheld his glory, the glory as of the Only-Begotten of the Father.

The Person of the Son of God therefore remaineth unchanged and one, though he hath two natures, keeping his own, and taking ours. He cometh on earth as man to be the restorer of man, but abideth all the while in his unchangeable Godhead. That Godhead which he shareth with the Father was not a whit the less almighty, nor did the form of a servant touch the form of God to derogate from it. The Most High and Everlasting Being, bending down for man's salvation, took the Manhood into his glory. Yet he ceased not to be that which he is from everlasting. Hence we see the only-begotten Son of God in one place confessing that the Father is greater than he, and in another declaring that he and the Father are One. This is an evident proof of the distinction of his two natures, and the unity of his Person. For he is inferior to the Father as touching his Manhood, and yet equal to the Father as touching his Godhead. Albeit, though he be God and Man, he is not two, but One Christ.

"When thou wast born all ineffably of a Virgin, then were the Scriptures fulfilled; thou camest down like the dew upon the fleece of wool, to bring salvation unto all mankind ; we praise thee, O our God."
- Second antiphon, Vespers.

"O God, who by the child-bearing of a pure Virgin hast bestowed upon all mankind the rewards of everlasting life : grant, we beseech thee ; that we may know the succour of her intercession, through whom we have been found worthy to receive the Author of life, even Jesus Christ thy Son our Lord : Who liveth and reigneth with thee."
-Collect of the day.