It just so happens that on the twenty-fifth of December in the Roman Empire there was a pagan holiday that was linked to mystery religions; the pagans celebrated their festival on December 25. The Christians didn’t want to participate in that, and so they said, “While everybody else is celebrating this pagan thing, we’re going to have our own celebration. We’re going to celebrate the thing that’s most important in our lives, the incarnation of God, the birth of Jesus Christ. So this is going to be a time of joyous festivities, of celebration and worship of our God and King.” R.C. Sproul (from, Is Christmas a Pagan Holiday?)