One would think that if anyone’s date of birth were remembered exactly, it would be that of our Savior, Jesus Christ. Unfortunately, the gospels do not pinpoint the date of Christ’s birth. The reason is probably that the focus of the gospels is on the kerygma or mystery of redemption — the passion, death and resurrection of Christ. This focus is also probably why St. Mark’s Gospel does not even include the Christmas story, but begins with the Baptism of the Lord at the River Jordan. Easter, on the other hand, can be better dated because of its concurrence with Passover.
Prior to the legalization of Christianity by the Emperor Constantine in the year 313, no universal date or even formal celebration of Christmas is found. For instance, Origen (d.255), St. Irenaeus (d. 202), and Tertullian (d. 220) do not include Christmas or its date on their lists of feasts and celebrations.
After legalization, the Church was better able to establish ;universal dates of feasts and to organize the public celebration. Moreover, we now see the Church addressing controversies concerning Jesus as true God and true man and how He entered this world. Such concern would focus more attention on the importance of celebrating Christmas, the birth of our Lord.
On the more practical side of this issue, Roman pagans used to gather at the hill where the Vatican is presently located to commemorate the “Birth of the Unconquered Sun” This pagan feast was celebrated throughout the Empire either on Dec. 25 (according to the Julian Calendar) or on Jan. 6 (according to the Egyptian calendar). Although not proven with certainty, some historians credit Constantine, who declared Sunday as a day; of rest in the Empire, with replacing the pagan festival with that of Christmas. Interestingly, since the 200s, Jesus was honored with the title, “Sun of Justice.”
Somehow all of these elements converged to the formal celebration of Christmas on Dec. 25. For instance, Christmas was celebrated in Rome by Pope Liberius (352-66) on Dec. 25. On Dec. 25, 379, St. Gregory Nazianzus preached a Christmas sermon in Constantinople. In the Cathedral of Milan, St. Ambrose (d. 397) celebrated Christmas. Therefore, by; the year 400, generally, the birth of Christ was set on Dec. 25 with the exception of Palestine, where it was celebrated on Jan. 6 until the mid-600s, when it was then transferred to Dec. 25.
As an aside, the Feast of the Epiphany also emerged in Gaul (the Roman province of present-day France) about the year 361. This feast was moved to Jan. 6, which remains the official date.
While the concern for exact dating may preoccupy us at times, I believe the most important point is celebrating the birth of our Lord. Remember that the title “Christmas” is derived from the Old English title “Cristes Maesse” which means “The Mass of Christ.” This Christmas, may we lift up our hearts at the Holy Sacrifice of the Mass and receive our Lord, born into our souls through the grace of the Holy Eucharist.
Source: Saunders, Rev. William. “The First Christmas.” Arlington Catholic Herald.