Why is Christmas on December 25th?

There are ten federal holidays in the United States in 2012, in addition to the fifty-four Sundays, which are specifically named in the Constitution as days of rest from Government work. Thanksgiving is always on the fourth Thursday in November, and the rest all fall on a Monday--with one sole exception. Christmas falls on December 25, a Tuesday.

What is it about December 25 that would make it the last  fixed holiday on the government calendar?

Well, for many centuries December 25 has been the date that Christians celebrate the Birth of Christ. Now, Eastern Christians are famous for observing this celebration on the 6th of January, but this is nothing more than the perpetuation of the December 25th celebration despite the secular adoption of the Gregorian calendar.

And this date has been observed for far longer than the schism between the Eastern and Western churches. In what is the earliest extant reference to what is now known as Christmas, the date on which the birth of Christ occurred was recorded, in Greek, by a writer named Hippolytus of Rome, in his Commentary on Daniel:

“For when the times from the foundation of the world and from Adam are reckoned, they furnish this matter quite clearly to us who seek an answer. For the first advent of our Lord in the flesh, when he was born in Bethlehem, eight days before the kalends of January [December 25th], the 4th day of the week [Wednesday], while Augustus was in his forty-second year, [3BC] but from Adam five thousand and five hundred years. He suffered in the thirty third year, 8 days before the kalends of April [March 25th], the Day of Preparation, the fifteenth year of Tiberius Caesar [30 AD], while Rufus and Roubellion and Gaius Caesar, for the 4th time, and Gaius Cestius Saturninus were Consuls. And so it is absolutely necessary for six thousand years to be fulfilled, so that the Sabbath rest may come, the holy day, in which God rested from all his works which he began to do. And so from the generation of Christ it is necessary to count the remaining five hundred years to the consummation of the six thousand years, and in this way the end will be."

 This dates back to the first decade of the third century; a full hundred years before the State took over the Church. Obviously the Christian observance of Christmas goes way, way back: but why? There is nothing in the Scripture itself to give us the exact year, much less the exact day, when Jesus was born. So why was it so important to Christians that they know when it was?

Well, here's a new idea I just ran across. Whether it's factual or not, I don't know; but it does appear to account for the evidence. Creation Ministries International posted this on their website:

The real source of the 25 December date is an extra-biblical Jewishtradition, called the ‘integral year’. This means that a prophet’s lifespan would be an exact number of years, so he would die on an anniversary of his conception, the real beginning of life. Jesus’ death was calculated as March 25^th by the Western church, and April 6^th by the Eastern Church. Therefore this same date was celebrated as the date Christ was conceived. Nine months later is December 25^th or January 6^th, and the latter date is still celebrated in the Eastern Orthodox church (and many branches of the Western church celebrate ‘Epiphany’ on the same day, now to commemorate the arrival of the magi and their three gifts).

Actually, this again is just the effect of the adoption of the Gregorian calendar by the Western Church.

Continuing on in Hippolytus, we can see that, like most chronographers, he did have an agenda:

 24.5. But because in the fifth and a half time the Savior arrived in the world bearing the incorruptible ark, that is his own body, John says, “and it was the sixth hour,” so that half of the day may be demonstrated, a day of the Lord is like thousand years.  And so the half of these is five hundred
years.
24.6 . . . .Because after the people returned from Babylon four hundred and thirty and four years occurred until the generation of Christ, it is easy to perceive what has been set before.  32.2. For since the first covenant with the sons of Israel was given after four hundred and thirty-four years, it is absolutely necessary for the second also likewise to be determined in the same time, so that it may be expected by the people and may be easily recognized by the believers.

There's one more thing to consider: The reading of Matthew 1:18.

Ἰησοῦ χριστοῦ ἡ γέννησις  --Majority reading in Greek;  Latin version corresponds; "birth of Jesus"
Ἰησοῦ Χριστοῦ ἡ γένεσις   --Reading of the oldest papyri & uncials, corresponding to "beginning" in some Coptic & Syriac manuscripts; "conception of Jesus"

Hippolytus uses the term “genesis (γένεσις) of Christ,” and it's clear that this refers to His conception, not birth. From a conception date of March 25 (the anniversary date of Creation, observed for many centuries in Christendom as New Years Day, having been fixed at a time when this Julian date corresponded to the spring equinox) derives the date of Jesus’ birth as December 25.

I should add that although there is a bit of discrepancy amongst the various medieval manuscripts of Hippolytus, a statue located at the entrance of the Vatican contains a canon-table self-dated rather precisely to the beginning of 222 A.D. On it is Hippolytus' date for Christ's conception: Wednesday, April 2, 2 B.C. So whilst Hippolytus and his copyists down through the ages did play around a bit with the precise year of Christ's birth (4 BC is the critical consensus, as adopted by Ussher), and sometimes confused it with the date of his conception, Wednesday, December 25, 3 BC can be nailed down as the original date.

UPDATE:
"It was not the visible sun, but its invisible Creator who consecrated this day for us, when the Virgin Mother, fertile of womb and integral in her virginity, brought him forth, made visible for us, by whom, when he was invisible, she too was created. A Virgin conceiving, a Virgin bearing, a Virgin pregnant, a Virgin bringing forth, a Virgin perpetual. Why do you wonder at this, O man?"

So wrote Augustine in Sermons 186:1, indicating--it would appear--that Jesus was born on a Sunday.

UPDATE:
It turns out there's a history of Presidential Executive Orders giving federal workers extra time to goof off either the day before, or the day after Christmas, whenever doing so would prolong the weekend.  President Obama provided a half-day off on Thursday, Dec. 24, 2009, and a full-day Monday Dec. 24, 2012 and Friday, Dec. 26, 2014. President George W. Bush provided a half-day holiday on Wednesday, Dec. 24, 2002, as well as several full days off the day before or after Christmas: Tuesday, December 24, 2001, Thursday, December 26, 2003, Tuesday, December 24, 2007, and Thursday, December 26, 2008.