Today is Christmas Day. There is, as always, a lot of talk about "the reason for the season". The Christians will tell you that it's Jesus (and a vocal minority will say that it is only Jesus), many Non-Christians will point out that Christmas steals rather heavily from earlier Roman and northern European Pagan traditions, and smart-alecks will say that the reason for the season is axial tilt.
I'd like to go mid-range here, not back as far as axial tilt, but farther back than the usually cited Pagan traditions.
On most parts of the planet, winter is a time of shortage - the plants are not fruiting or nutting, some animals are hibernating, the cold outside makes gathering food a difficult proposition especially in climates where it snows, shorter days provide less daylight in which to do any form of outside work (and, depending on the environment, may provide opportunities for predators), and people who had been free to come and go from each other's company are forced to deal with each other more closely than in other parts of the year. For many cultures, winter is a time of enforced inactivity, it is a time when the days have become short and cold, and a time when social stresses may increase due to people being closer together. Mid-winter especially is often a prelude to the hunger of late winter.
It is, therefore, no wonder that people choose to have celebrations in mid-winter. The solstice may be one reason - the realization that days will begin getting longer and warmer is certainly cause for celebration, but the social an psychological problems that stem from cold, dark days and nights and increased population density in the settlement require a release, and a joyful, celebratory release is generally preferable to a violent, destructive release.
The celebration may take many forms - communal feasting, many day long displays of the shaman's power, ceremonies intended to restore the sun and/or renew the world, the giving of gifts to restore social bonds between individuals and thus strengthen the community - regardless of the form, the basic purpose is the same: blow off steam, get everyone on a good footing with each other, and help people to deal with the stresses of the cold months.
Depending on what one takes as the cut-off point to count a creature as a member of our species, humans have been around for at least 500,000 years, and it is likely that winter celebrations or ceremonies have been part of our cultural make-up for at least that long, and perhaps longer (we know little about the religious and ritual lives of modern humanities direct ancestors).
So, yes, Christmas borrows it's time from Saturnalia and its finery from northern European Paganism, but even these traditions borrow from much earlier predecessors. By celebrating the winter festival, whether you call it Christmas, Hanukkah, Yule, Kwanzaa, or anything else, you are taking part in one of humanity's oldest rites.
Enjoy it, we do it for a reason. I hope all of you are having a good day today, regardless of what you call it.