What is probably the first mention of Jesus’ birth on December 25 dates back to the 3rd century, when Hippolytus of Rome wrote, “The first advent of our Lord in the flesh, when he was born in Bethlehem, was December 25th, Wednesday” (Commentary on Daniel, tr. by Schmidt, T. C., 2010, Book 4, 23.3). The earliest mention of some sort of observance on that date is in the Philoclian Calendar, representing Roman practice, of the year 336.
People have put forward various reasons for the choice of December 25 for the birth of Jesus:
1) December 25 is nine months after March 25, which the historian Sextus Julius Africanus and the early church father Tertullian calculated to be the date of the Passover on which Jesus was conceived (see Tertullian’s Adversus Judaeos, Ch. VIII). This reckoning was based on the tradition that Jesus was conceived and died on the same calendar day.
2) According to another tradition, March 25 was the anniversary of the creation of the world. Jesus’ conception on that date would lead to His birth on December 25.
3) December 25 coincided with a pagan festival celebrating the winter solstice. The church thereby offered people a Christian alternative to the pagan festivities and eventually reinterpreted many of their symbols and actions in ways acceptable to Christian faith and practice.
December 25 has become more and more acceptable as the birth date of Jesus. However, some argue that the birth occurred in some other season, such as in the fall. Followers of this theory claim that the Judean winters were too cold for shepherds to be watching their flocks by night. History proves otherwise, however, and we have historical evidence that unblemished lambs for the Temple sacrifice were in fact kept in the fields near Bethlehem during the winter months. With that said, it is impossible to prove whether or not Jesus was born on December 25. And, ultimately, it does not matter.
The truth is we simply don’t know the exact date of our Savior’s birth. In fact, we don’t even know for sure the year in which He was born. Scholars believe it was somewhere between 6 BC and 4 BC. One thing is clear: if God felt it was important for us to know the exact date of the Savior’s birth, He certainly would have told us in His Word. The Gospel of Luke gives very specific details about the event, even down to what the baby was wearing–“swaddling clothes”—and where He slept—“in a manger” (Luke 2:12). These details are important because they speak of His nature and character, meek and lowly. But the exact date of His birth has no significance whatsoever, which may be why God chose not to mention it.
The fact is that He was born, He came into the world to atone for our sins, He was resurrected to eternal life, and He’s alive today. This is what we should celebrate, as we are told in the Old Testament in such passages as Zechariah 2:10: “‘Shout and be glad, O Daughter of Zion. For I am coming, and I will live among you,’ declares the LORD.” Further, the angel that announced the birth to the shepherds brought “good news of great joy that will be for all the people” (Luke 2:10). Surely here is the cause for celebration every day, not just once a year.