Pastor Joseph Abrahamson has started a fascinating series on why the church celebrates Christmas on December 25 and when this started. He includes a number of links and references, and he critiques the notion that Christians co-opted a pagan holiday.
I was fascinated by the evidence he offers about the Feast of the Annunciation (when the angel appeared to Mary and she conceived by the Holy Spirit), which was celebrated on March 25, a date established before 200 A.D. The church added nine months from that date, which gives us the Baby so conceived being born on December 25.
I have heard it said that the date of Christ’s birth was once considered to be March 25, but that claim is based on a mistranslation and misunderstanding of “genesis.” Rev. Abrahamson quotes Clement of Alexandria, in his “Stromata,” dated between 193 and 215 A.D.:
And there are those who have determined our Savior’s genesis
not only the year, but even the day, which they say took place
in the twenty-eighth year of Augustus on the 25th of Pachon.
Rev. Abrahamson comments:
The important line is “our Savior’s genesis.” The month of Pachon in the Egyptian calendar at that time corresponded to March in the Julian Calendar.
Christ’s genesis, or conception on the 25th of Pachon was in what our calendar would equate with March 25th. The celebration of Christ’s birth would be nine months later: December 25th, in our calendar. ANF 2:333 translates “birth” rather than “conception”. The translation of “genesis” as conception is consistent with Clement’s usage of this word in other contexts, for example:
“It is not therefore frequent intercourse by the parents, but the reception of it [the seed] in the womb which corresponds with genesis.” (Clement of Alexandria Stromata 22.214.171.124)
So the early church believed that a person’s “genesis” begins with conception and not with birth. That’s an important point for the pro-life cause today.