Christmas is a Christian festival which celebrates the nativity of Jesus Christ. The nativity was not celebrated by the first Christians. The exact date of the birth of Christ is always unknown and at the 3rd century one celebrated the nativity in April or November. It is Constantin, into 333, who decided to fix a single date to celebrate the birthday of Jesus.
The Libère pope officially fixed the festival of Christmas at December 25. This choice is explained by the will to promote the rise of Christianity and to replace popular holidays and pagan celebrated on December 25 (festivals of Mithra to introduce the winter solstice).

In the Christian tradition, the evening of Christmas is one night devoted primarily to the family and God. The families meet and evacuate, the space of one evening, the problems involved in the life of every day. Christmas is one evening when the families meet and link themselves for a common cause: the recall of God.
Nowadays, Christmas is for much a festival in lucrative matter. Christmas left the strictly religious framework. The Christians practitioners continue to celebrate Christmas as a recall of the nativity, with the Father Christmas. But more and more of people, who they are atheistic or of different confessions, start to celebrate Christmas.

Christmas that they celebrate has a completely different symbolic system. The latter stick to traditions which do not have anything any more monk. Gifts, fir trees, garlands, Santa claus, etc. You buy decorations for your house, and your fir trees, lights and so on.
These derive involve a big rise of the economy and in parallel, a strong fall of the fastener which binds Christmas to Jesus. The laic companies denature the monk by adapting it when that creates a economic contribution. Industry became the door word of Christmas, leaving the Church to the second plan.