We all know what Christmas is. And we all know (I hope) that the Bible does not mention Christmas. Nor does it mention snowmen, holly, ivy or reindeer.
What the Bible does mention is Christ's birth. Both Matthew and Luke go into some detail about the circumstances. Although the two of them see the events from different viewpoints, they agree on a few central details: Mary's virgin innocence, Joseph's passive involvement, the appearance of an angel, the birth in Bethlehem. The remaining details - the magi, King Herod, the shepherds, the journeying, the manger - reflect what Matthew and Luke saw as significant parts of the story. For John, on the other hand, the significance could be summed up in eight words: "the Word became Flesh and dwelt among us" - no need for further detail.
When the apostles went out to tell the world about Jesus, it was not in the first place to tell people about the happenings in Bethlehem. Paul reminded the Corinthians: "I handed on to you as of first importance what I in turn had received: that Christ died for our sins in accordance with the scriptures, and that he was buried, and that he was raised on the third day in accordance with the scriptures..." (1 Cor 15:3-4) The events in Jerusalem formed the central message. But of course as a prelude Christ became human, one of us, and Paul recalls to the Philippians the significance of this, perhaps quoting an early hymn: "Though he was in the form of God, he did not regard equality with God as something to be exploited, but emptied himself, taking the form of a slave, being born in human likeness. And being found in human form, he humbled himself and became obedient to the point of death - even death on a cross." (Phil 2:6-8)
Christianity is (or should be!) a religion of joy. For the early followers of Christ, joy lay in forgiven sins, and above all in the joy of the resurrection. They celebrated this joy when they met each week on the day of the resurrection. But at Christ's birth too, the angel gave the shepherds "good news of great joy for all the people: to you is born this day in the city of David a Saviour, who is the Messiah, the Lord." (Luke 2:10-11)
Over the early centuries of the church, the practice grew up of remembering holy people, often on a significant anniversary. Sometimes people would meet at a church associated with a particular person. But for Jesus, there was no "significant anniversary". Nobody knew when he was born (and if the shepherds were out with their flocks at night, it would not have been "the deep mid-winter"!) The events of his life had no calendar date, except for his crucifixion and resurrection - and even those had to be dated by the sun and moon together, where the calendar used in the Roman empire measured only by the sun.
So the practice grew up of remembering Jesus' birth on a day when people in the empire rejoiced - when in the depths of winter the days started to grow longer again, when the sun started to grow in strength. In the same way, people celebrated John the Baptist's birth in mid-summer (where John's saying "He must increase and I must decrease" (Jn 3:30) reflected itself in the duration of daylight), and the angel's announcement to Mary on 25 March, which remained the start of the new calendar year in England until 1753.
25 December is known in German as Weihnachten, the old plural form recalling that the whole season was holy (and we still talk of the twelve days of Christmas). In Scandinavia, the name we know in English as Yule recalled a pagan God, and was the name of a whole month, but over time, Yuletide lost its pagan significance and came to refer to our Christian festival. The French Noël and the Italian Natale stem from the Latin word for "birth" - not Christ's birthday, but the day for recalling Christ's incarnation!
In English, the word Christmas goes back to the earliest days of the language - Christ's Mass, Christ's Festival. In addition to Christmas, a few British traditional festivals retain names in English ending in -mas: Candlemas (2 February), Lammas (2 August) (the loaf-mass, or Harvest Festival), Michaelmas (29 September). These were all days which marked the beginning or the ends of seasons. They were celebrated with fairs, with processions, with local traditions. They were of secular as well as religious significance, and after the Reformation many of them lost their focus, and became little more than days on which rental payments were due. But one of them never lost its significance. Christ was the focus of Christmas, and remains so today.
HD