The origin of Christmas lies in the commemoration of the birth of Jesus Christ. Over time, December 25th was chosen as the day to celebrate this event and annual mass services were conducted to honor Jesus' birth.
The festival of Christmas, although now closely associated with Christianity, actually has its roots in the pagan Roman winter solstice festival known as Saturnalia. As Christianity spread throughout the Roman Empire, the Church adapted this existing festival into a Christian celebration, linking it to the birth of Jesus.
It is important to note that the Bible does not provide a specific date for Jesus' birth, nor does it mention a celebration for this event. Thus, the Christmas holiday as we know it today is a result of the Christianization of a pre-existing Roman mythological festival.
Source:百度百科-圣诞节
