I know it's a little late for this particular topic in the West, but today is the day Christmas is celebrated among the Eastern churches who still use the Julian calendar, so I don't feel too badly about it. This also means that my fellow procrastinators who like to delay taking down their Christmas lights get a reprieve! 😅
For most of my life, I've been taught that Jesus was likely born in the Spring, because Judean shepherds didn't take their sheep out to pasture in winter. The old explanation of why we celebrate Christmas on December 25 was that the Romans associated the time with the pagan festivals of Saturnalia and Sol Invictus, and so the Church transformed (or co-opted) the dates to celebrate Christ instead.
This never really bothered me, because if Christ really is God and can bring transformation to someone like me, then He can certainly redeem any, and all, days of the year. What is important to me is the Incarnation, the belief that God the Son, the Divine Logos ("Word") took on flesh as man and dwelt among us, lowering Himself, so that we - as Christ's brothers and sisters - may be raised into the household of God. That's what Christmas is all about, no matter which day of the year it is celebrated.
But, as I've studied this topic more and more over the years, out of historical curiosity as much as anything else, the more convinced I've become that Jesus *was* actually born on or around Dec. 25 and that the available biblical and historical clues support this conclusion (and I'm indebted for this information to more sources than I can list here).
Here's what we can discover from a careful look at Scripture:
1) The angel Gabriel announced to the priest Zechariah the conception of his son, John, when Zechariah was offering incense in the Temple during the alloted time for the priestly division of his clan: Abijah (Luk. 1:5, 8-11). Elizabeth his wife became pregnant immediately after.
1 Chr. 24:5-18 says the descendants of Abijah would serve in the 8th rotation of the year, during Yom Kippur (the Day of Atonement, ~Sep. 22-30).
2) The angel Gabriel announced the conception of Jesus 6 months later to Mary (Luk. 1:26), around March 25.
3) Jesus was likely born ~9 months later, around December 25 (cf. John Chrysostom's "On the Day of the Birth of Our Savior Jesus Christ").
So what does it mean for the shepherds who received the angels' message that a Savior had been born to them in the City of David (Luk. 2:8-20)? Was this an anachronistic mistake on the part of the author of the Gospel? I don't think so. As it turns out, according to the Mishnah (Shekalim 7:4), sheep to be offered at the Passover could be found as early as 30 days prior to the festival in the fields as far as Migdal Eder (near Bethlehem, cf. Gen. 35:19-21) from Jerusalem in any direction. Since this would be mid-February, it shows sheep could be found in the area in winter, as Judean winters are often very mild; and shepherds still pasture their sheep in the middle of winter near Bethlehem today.
Even the old argument that Christians stole the date from the pagan celebration of Sol Invictus doesn't hold water on careful historical inspection. The Roman cult of Sol Invictus was instituted on Dec. 25, 274 by the Emperor Aurelian, and its last celebration was in 387.
But Hippolytus of Rome, writing in his Commentary on Daniel, first associates the Annunciation of Jesus' conception to Mary with March 25. Since Hippolytus died around 235 AD, even if he wrote this commentary in the last year of his life, the first written text associating Jesus' birth with December 25 comes a full 40 years before the first celebration of Sol Invictus.
And while it's true that the Roman winter festival Saturnalia was celebrated around this time, that festival was celebrated on Dec. 17.
Rather than Christianity appropriating the holiday from Roman pagans, it appears the pagans may have tried to stem the rampant growth of Christianity by creating their own festival of Sol Invictus in order to directly compete with Jesus' birth.