A festival close to the winter solstice has been celebrated, quite literally, from time immemorial. At a time when humanity was entirely dependent on the seasonal cycle for every item of life and with no understanding of the science, the disappearance of the sun and its life-giving properties and then its return was not a certainty and a celebration that was both a welcoming and a celebration of return makes absolute sense. The mid winter celebration was symbolic then remains so.
Why do christians celebrate the birth of Christ on 25th December? For the same reason that our pre-historic ancestors celebrated the return of the sun. It commemorates that when the world was in the darkness of ignorance of God and his goodness, a child was born in the humblest of circumstances to bring light and the promise of a new spring to the world. Not everyone shares that religious belief but its symbolic rationale is obvious.
You do not need to be a Christian to celebrate Christmas. I spent part of my childhood in south east Asia and in all the countries we lived in we joyously celebrated everybody's festivals. Chinese New Year, Diwali, Christmas, all the Muslim festivals, that had different names in different countries, were all celebrated by Christian, Hindu, Muslim and every other religion. I loved it.
