Across almost every culture in the northern hemisphere that was formed in a temperate climate there is a feast within a week or two of the first day of winter, which acted as the last feast before several long hard months where food was scarce do to winter. In many religions the calibration of their religion happens at (approximately) this time to coincide with the feasting.

Now, early Christian missionaries were very clever and (rather than try to convert pagans through force) chose to adopt the traditions of the pagans and convince them that their beliefs and celebrations were really a part of Christianity; and as a result many traditions that have no real basis in Christianity have spread throughout the world as part of Christian celebrations, and the Catholic church has a lot of saints which were (at one point in time) pagan gods.

Christmas was originally Pagan, a celebration of the Winter Solistice. Its as a lot easier to attract Pagans if Christianity shared holidays and ideas with them. There were a lot of things about Christianity that changed from the time of Jesus to the time when Christianity became the major religion in Rome.