You know how it is when some great king enters a large city and dwells in one of its houses; because of his dwelling in that single house, the whole city is honored, and enemies and robbers cease to molest it.
Even so is it with the King of all; He has come into our country and dwelt in one body amidst the many, and in consequence the designs of the enemy against mankind have been foiled and the corruption of death, which formerly held them in its power, has simply ceased to be.
For the human race would have perished utterly had not the Lord and Savior of all, the Son of God, come among us to put an end to death.
That passage from Athanasius' De Incarnatione Verbi Dei hints at why we get to experience the "Word of the Father, now in flesh appearing." John 1, which we will be studying at Urbana, does likewise...
He was in the world, and though the world was made through him, the world did not recognize him. He came to that which was his own, but his own did not receive him. Yet to all who received him, to those who believed in his name, he gave the right to become children of God— children born not of natural descent, nor of human decision or a husband's will, but born of God.
The Word became flesh and made his dwelling among us. We have seen his glory, the glory of the One and Only, who came from the Father, full of grace and truth.
John testifies concerning him. He cries out, saying, "This was he of whom I said, 'He who comes after me has surpassed me because he was before me.' " From the fullness of his grace we have all received one blessing after another. For the law was given through Moses; grace and truth came through Jesus Christ. No one has ever seen God, but God the One and Only, who is at the Father's side, has made him known.
Adoption. Redemption. Revelation. "Word of the Father, now in flesh appearing."
So, that's why some old, dead guys think we have Christmas.
Here're some other opinions:
How December 25 became Christmas - the origins of the date and festival
O Holy Night...sort of - "Jesus was born and so I get presents"...Eric Cartman's take on Christmas
Advent Conspiracy - These folks think that since it's Jesus' birthday, he should get the presents and that having this attitude would help us, especially in America, to recover what they call "the scandal of Christmas."