Of course many will argue that it is not the time of His birth, stating that Christ was born in the summer - and they are at least partially right. The Gospel according to Luke, however still explains why it is nevertheless time to celebrate. First going back to the conception of John the Baptist:
Luke 1: 5, 11-13 wrote:There was in the days of Herod, the king of Judaea, a certain priest named Zacharias, of the course of Abia: and his wife [was] of the daughters of Aaron, and her name [was] Elisabeth...
...And there appeared unto him an angel of the Lord standing on the right side of the altar of incense.
And when Zacharias saw [him], he was troubled, and fear fell upon him.
But the angel said unto him, Fear not, Zacharias: for thy prayer is heard; and thy wife Elisabeth shall bear thee a son, and thou shalt call his name John.
What is interesting back in verse 5 is that it states that Zacharias was of the course of Abia, which states for us the time of year of this occurrence. “Course of Abia” refers to the division of the priests by King David in 1 Chronicles 24. The division was into 24 one week courses, served twice per year (the remaining weeks were those of the great feasts, in which all congregated at the temple). The course of Abia was the eighth, which was served each year from June 15-19 (and mid-December, but this is the June course).
Luke 1:23-25 wrote:And it came to pass, that, as soon as the days of his ministration were accomplished, he departed to his own house.
And after those days his wife Elisabeth conceived, and hid herself five months, saying,
Thus hath the Lord dealt with me in the days wherein he looked on [me], to take away my reproach among men.
Zacharias needed some travel time to return home, naturally, and so John was therefore conceived in late June. Now we come to the Conception of Christ:
Luke 1:26-37 wrote:And in the sixth month the angel Gabriel was sent from God unto a city of Galilee, named Nazareth,
To a virgin espoused to a man whose name was Joseph, of the house of David; and the virgin's name [was] Mary.
And the angel came in unto her, and said, Hail, [thou that art] highly favoured, the Lord [is] with thee: blessed [art] thou among women.
And when she saw [him], she was troubled at his saying, and cast in her mind what manner of salutation this should be.
And the angel said unto her, Fear not, Mary: for thou hast found favour with God.
And, behold, thou shalt conceive in thy womb, and bring forth a son, and shalt call his name JESUS.
He shall be great, and shall be called the Son of the Highest: and the Lord God shall give unto him the throne of his father David:
And he shall reign over the house of Jacob for ever; and of his kingdom there shall be no end.
Then said Mary unto the angel, How shall this be, seeing I know not a man?
And the angel answered and said unto her, The Holy Ghost shall come upon thee, and the power of the Highest shall overshadow thee: therefore also that holy thing which shall be born of thee shall be called the Son of God.
And, behold, thy cousin Elisabeth, she hath also conceived a son in her old age: and this is the sixth month with her, who was called barren.
For with God nothing shall be impossible.
So then six months after Elisabeth conceived, the story that we all recognize begins, as the angel comes to the Virgin Mary. This tells us that in December that we celebrate not the birth, but the conception, and we do have reason to celebrate as in verse 41: And it came to pass, that, when Elisabeth heard the salutation of Mary, the babe leaped in her womb; and Elisabeth was filled with the Holy Ghost.
When Mary came to visit her cousin, John, six months in Elisabeth's womb leaps with joy (!) as he realized that Christ though yet unborn was present on Earth on that day in late December.
Now this still leaves the "loophole" that 1:5 could have referred to the second course of Abia. The difference between the two would, once you add up the months, be the difference between a late summer birth for Christ, and a late winter birth. Luke 2:8 tells of the shepherds in the fields, which would not have been the case in winter. This means June course of Abia and conception of John, December conception of Christ, September birth.
Anyway, I'm not the best at this, and I could link to those who are better, but I'm not here to link to preachers, but to wish you all a Merry Christmas. So if the way I explained this wasn't clear, then just read the first chapter of Luke, or Google "Course of Abia," or just sit back, relax, and enjoy some eggnog. The bottom line is that this is the season in which Christ came to join us on Earth, and is a season for celebration. So, take some time out from the exciting bowl season to have a happy Christmas as well.