Sol Invictus
Today is the winter solstice, the day which has the least sun out of the whole year. The Romans used to celebrate the birth of Sol Invictus, the Unconquerable Sun on the winter solstice because they had hope that even though the sun appeared to be weakening and dying all winter long, after the winter solstice the sun only got stronger and stronger into the new year. In those days they celebrated the winter solstice on December 25, and it is speculated that when the Romans adopted Christianity, they changed from celebrating the birth of the Unconquerable Sun to the birth of the Unconquerable Son, Jesus Christ. You may think that this might cheapen the meaning of Christmas since it's basically continuing on a pagan tradition, but a celebration of the birth of the source of all light and warmth is practically the definition of the Spirit of Christmas. Just like the sun returns to its full strength and glory after dying during the winter solstice, Christ will return in His full strength and glory. Just as winter can never conquer the sun, so too can evil never conquer the Son. The fact that Christmas is celebrated on the same day as the celebration of Sol Invictus should add to and enrich our understanding and appreciation of the true meaning of Christmas.