All time is God's time. When the eternal Word assume human existence in the Incarnation, he also assumed temporality. He drew time into the sphere of eternity. At first it seems as if there can be no connection between the "always" of eternity and the "flowing away" of time. But now the Eternal One himself has taken time to himself. In the Son, time co-exists with eternity. God's eternity is not mere time-lessness, the negation of time, but a power over time that is really present with time and in time. In the Word incarnate, who remains man forever, the presence of eternity with time becomes bodily and concrete.
[...] The feast of Christ's birth on December 25 - nine months after March 25 [the day that the early "Church honored both the Annunciation by the angel and the Lord's conception by the Holy Spirit in the womb of the virgin"] - developed in the West in the course of the third century, while the East - probably because of a different calendar - at first celebrated January 6 as the birthday of Christ. It may also have been the response to a feast of the birth of the mythical gods observed on this day in Alexandria. The claim used to be made that December 25 developed in opposition to the Mithras myth, or as a Christian response to the cult of the unconquered sun promoted by Roman emperors in the third century in their efforts to establish a new imperial religion. However, these old theories can no longer be sustained. The decisive factor was the connection of creation and the Cross, of creation and Christ's conception. In the light of the "hour of Jesus", these dates brought the cosmos into the picture. The cosmos was now thought of as the pre-annunciation of Christ, the Firstborn of creation (cf. Col. 1:15). It is he of whom creation speaks, and it is by him that its mute message is deciphered. The cosmos finds its true meaning in the firstborn of creation, who has now entered history. From him comes the assurance that the adventure of creation, of a world with its own free existence distinct from God, does not end up in absurdity and tragedy but, throughout all its calamities and upheavals, remains something positive. God's blessing of the seventh day is truly and definitively confirmed. The fact that the dates of the Lord's conception and birth had a cosmic significance means that Christians can take on the challenge of the sun cult and incorporate it positively into the theology of the Christmas feast. There are magnificent texts that express this synthesis. For example, St. Jerome in a Christmas sermon says this: "Even creation approves our preaching. The universe itself bears witness to the truth of our words. Up to this day the dark days increase, but from this day the darkness decreases...The light advances, while the night retreats." Likewise, St. Augustine, preaching at Christmas to his flock in Hippo: "Brethren, let us rejoice. The heathen, too, may still make merry, for this day consecrates for us, not the visible sun, but the sun's invisible Creator." (Ratzinger 2000:92, 107-108)
In the beginning was the Word, and the Word was with God, and the Word was God. He was in the beginning with God. All things came into being through Him, and apart from Him nothing came into being that has come into being. In Him was life, and the life was the Light of men. The Light shines in the darkness, and the darkness did not comprehend it. (John 1:1-5)
For [the Father] rescued us from the domain of darkness, and transferred us into the kingdom of His beloved Son, in whom we have redemption, the forgiveness of sins. He is the image of the invisible God, the firstborn of all creation. (Colossians 1:13-15)
The heavens are telling of the glory of God;
And their expanse is declaring the work of His hands.
Day to day pours forth His speech,
And night to night reveals knowledge.
There is no speech, nor are there words;
Their voice is not heard.
Their line has gone out through all the earth,
And their utterances to the end of the world.
In them He has placed a tent for the sun,
Which is as a bridegroom coming out of his chamber;
It rejoices as a strong man to run his course.
Its rising is from one end of the heavens,
And its circuit to the other end of them;
And there is nothing hidden from its heat. (Psalm 19:1-6)
Ratzinger, Joseph. (2000). The Spirit of the Liturgy (J. Saward, Trans.). San Francisco, CA: Ignatius Press.