“The Evangelical Dictionary of Theology” explains that the earliest Christians did not have a time when they regularly observed Christ’s birth. However, by the late fourth century it was generally celebrated in churches. December 25 became recognized as Christmas day because it provided a Christian alternative to pagan festivals related to the Roman god Saturn and the winter solstice.
The funny thing is that we all know if we read the Bible when Christmas should be, nine months after Gabriel told Mary she would become pregnant. She was told in late June or early July. That puts Christmas in late March or early April. Roman taxes were paid in spring, just like they are now here. Christmas can be celebrated anytime you want but The son of God was born in the flesh in the spring.