The middle of winter has long been a time of celebration around the world. Centuries before the birth of Jesus, the early civilizations celebrated light, fertility, and birth in the darkest days of winter. Most cultures rejoiced during the winter solstice, when the worst of the winter was behind them and they could look forward to longer days and extended hours of sunlight.
In ancient times, in the northern hemisphere, the end of December was a perfect time for celebration. At that time of year, the harvest was in and most of the livestock were slaughtered so they would not have to be fed during the winter. Furthermore, it was the only time of year when a supply of fresh meat was abundant; refrigeration did not yet exist. Not to mention, the wine and beer made during the year was fermented and ready for drinking.
Long before the beginning of Christianity, plants and trees that remained green all year had a special meaning for people in the winter. Just as people today decorate their homes during the festive season with pine, spruce, and fir trees, ancient peoples hung evergreen boughs over their doors and windows. In many countries it was believed that evergreens would keep away witches, ghosts, evil spirits, and illness.
In the Northern hemisphere, the shortest day and longest night of the year falls on December 21 or December 22 and is called the winter solstice. Many ancient people believed that the sun was a god and that winter came every year because the sun-god had become sick and weak. They celebrated the solstice because it meant that at last the sun-god would begin to get well. Evergreen boughs reminded them of all the green plants that would grow again when the sun-god was strong and summer would return.
Likely the most celebrated holiday in the world. Christmas today is a product of hundreds of years of modification, both secular and religious. Traditions from around the globe, having nothing at to do with God, have been modified to garner some semblance of holiness.