It never ceases how many “Christians” are so fast to join forces with atheists, pagans, and all manners of Christ-haters in hating Christmas.
Yes, it is true that the ancient Christians supposed at a date when to celebrate Christmas. But they did so for pious, sensible reasons having nothing to do with pagan celebrations.
The claim that Christmas was chosen to fall on In Sol Invictus is simply a Satanic slander. The opposite is true: Sol Invictus was celebrated in August, until moved to that year four centuries after Christ, by gnostics who wished to co-opt the Christian holiday into their pantheon. There has been some association with Sol Invictus and Christ, but this is likely a contrast, with Christ labeled the “Sun of Justice,” taking after Malachi 4:2, written centuries before Rome even adopted the worship of Sol. [”But for you who revere my name, the Sun of Righteousness will rise with healing in its wings. And you will go out and leap like calves released from the stall.”]
December 25th was chosen for Christmas for two reasons:
1. While the apostles may not have known Jesus’ birthday, they certainly knew of the day he died: The day before the Pharisees’ Passover, which was the day of the Essenes’ passover. This was calculated in antiquity to have fallen on March 25th. Great prophets were said to be conceived into the afterlife (died) on the day the day they were conceived into the world. Hence, March 25th is celebrated as the Feast of the Annunciation, when Christ was conceived. December 25th is nine months later.
2. The Feast of the Dedication of the Temple celebrates the return of the Spirit of God to dwell among Men. It’s the 8th day of Passover, and falls on the 25th of the month closest to December (Kislev). Christ declared that He was the Temple of the Living God. He traveled to Jerusalem at the time of the Feast of the Dedication in each of his three-year ministry. (In fact, that’s about the only basis for suggesting his ministry lasted three years.)
It makes sense that the Feast of the Dedication could celebrate his conception. Even if so, it’s a fine day to celebrate.
Many other arguments are quite spurious; For instance, it’s said shepherds wouldn’t be having their sheep out to pasture. But that’s based on weather we have now. During the Roman Warm Period, the existence of weather warm enough to pasture sheep is hardly proof that an event couldn’t fall on the 25th of Kislev, especially since 25 Kislev could be as early as mid-November.
Very good post about why December 25th could have been chosen as Christ's birthday. Another reason could be that it's the correct date. Scripture says shepherds were pasturing their flocks near Bethlehem. To pasture near Bethlehem means it was after the rains had started (November) and there had been a few weeks for the grass to grow.
Also-
The only indigenous breed of sheep in Lebanon, Jordan and Israel, the Awassi Sheep lamb with the new grass (as do nearly all pasture animals). "In... the principal lambing season of Awassi ewes is in ... Israel in December-January."