@aqswed: I live up north, we go winter camping with scouts unless it is under 0F, a lot colder than what those shepherds did, in basic tents and outside all day regardless of weather. Sure, we have blankets and cots, but people back then were pretty inventive too, the Roman Empire reached all the way up to Finland with soldiers being stationed in the Netherlands.
@Duran: it is in the Bible, Roman Catholic Bibles at least:
1 Maccabees 4:36–39
Describes the rededication of the temple and the decree to celebrate annually on the 25th of Kislev which in 2024 also falls on December 25th.
It is traditionally celebrated with a tree/bush in the home and lights and feasting. Does the symbolism re-appear elsewhere in other religions, off course, because some things always evolve to the same conclusion.
Christians were known to celebrate the day of the nativity as there is contemporary evidence as early as 200AD in North Africa. Origen also wrote about the celebration of the manger of Jesus in 215AD, as did Justin Martyr (100-165AD). So already in the first and second century Christianity do we see the nativity of Jesus being mentioned and venerated/celebrated, so the theory of pagan alignment much later in the Catholic Church is an outdated anti-historic idea which was much more recently introduced as a ‘fact’, however the Coptic and various other churches that were founded by other apostles as early as 42AD, ALSO celebrate Christmas (although in different forms liturgically).