I have been studying with the Witnesses, who state that December 25th probably wasn’t when Jesus was born. They reason that it would have been too cold for shepherds to be out with their sheep in December. They point to the fact that the 25th was in fact already celebrated as winter solstice and is just used now to make things simple. I would appreciate any information you may be able to give me.
There is partial truth to this view. The winter solstice, however, was December 21st, not 25th. In the Greco-Roman calendar December 25th was the festival of Saturnalia, a holiday during which masters became slaves and slaves became masters for a day. It was the day of reversals.

While it is possible that Jesus was born in the winter, this is far from certain, and the fact that the shepherds and sheep were out in the fields might well suggest the birth occurred during some other season of the year. If Jesus’ birth was heralded by a partial conjunction of planets, it might be possible to be more certain as to the time of year. But the Magi story in Matthew suggests something more supernatural than an ordinary cosmic event.
The church probably began to celebrate the birth of Christ when they did in order to replace pagan holidays with Christian ones. Beginning with the emperor Constantine, who converted to Christianity, there was a decided movement in this direction.
What we can say with certainty is that since Jesus was born during the reign of Herod the Great, and we know that Herod the Great died in or before 2 B.C., we also know that Jesus was not born right at the turn of the era (in the “year zero”). The monk who set up the calendar was clearly off a few years.
—Ben Witherington III