Leo was Bishop of Rome from 440 to 461. He is the only pope, aside from St Gregory, to be called the Great. He was an able administrator, diplomat, and preacher – among the many sermons of his that have survived are several that deal with the theology of Christmas. Here are some excerpts from these orations.
Let us be glad in the Lord, dearly beloved, and make merry with spiritual joy. For there has dawned for us the day of new redemption, of ancient preparation, and of eternal bliss. In this annual feast there is renewed for us the sacrament of our salvation, which was promised from the beginning, was accomplished in the fulness of time, and will endure for all eternity. (Homily 2,1.)
In assuming our nature, Christ became for us a ladder, so that through Him we can now ascend even unto Himself. (Homily 5,3.)
Let Catholic faith recognize the glory of the Lord in His humility; and let the Church, which is the body of Christ, exult in the sacraments of her salvation. For unless the Word of God had become flesh and had dwelt amongst us, unless the Creator Himself had descended to enter into communion with His creature and in His birth had restored the old man by a new beginning, death would have reigned from Adam even unto the end (Rom. 5:14), Irrevocable condemnation would have been all men’s lot, and the very fact of birth would have been unto all cause of perdition But He became a man of our race, that we might become partake of the divine nature. The birth that was His from the virginal womb, He made available to us in the baptismal font. He gave to water the same power that He gave to His mother. For the power of the Most High and the overshadowing of the Holy Spirit (Luke 1:35) which made Mary give birth to the Savior, likewise effect that water gives new life to the believer. (Homily 5,5.).
Although the infancy which the majesty of God’s Son did not disdain passed into the maturity of manhood, and although all the acts of humility undertaken for us ceased once the triumph of the passion and resurrection had been attained, yet today’s festival renews for us the sacred infancy of Jesus born of the Virgin Mary; and while we adore the birth of our Savior, we find that we are celebrating too the commencement of our own life. For the birth of Christ is the origin of the Christian race, since the birthday of the Head is the birthday of the body. (Homily 6.2)