December 25th is associated with the birth of many pagan gods, including Mithra, Horus, Zeus and Sol Invictus (to name a fraction). The Roman festival of Saturnalia would also end around this time.
Christianity adopted many of these Pagan myths and traditions into its own customs at around 400AD.
Today Christians express outrage that Christmas is losing its Christian roots. Which is ironic considering it was Christians that hijacked the holiday in the first place to make it easier to convert new followers.
Nevertheless, whatever you hold faith in (even if you hold faith in nothing), this time of year is a wonderful opportunity to share love with friends and family, commit acts of goodwill to those who are less fortunate (if you need a reason to do that in the first place) and it is a time for adults to find their inner child (or at least make merry at every chance to do so).
The “reason for the season” is actually the axial tilt! Regardless. Happy “Whatever doesn’t offend you” and may it be filled with debauchery like no other!