Consider these quotes from the Catholic Encyclopedia, 1911 edition, under “Christmas”: “Christmas was not among the earliest festivals of the Church…the first evidence of the feast is from Egypt.” Further, “Pagan customs centering around the January calends gravitated to Christmas.” Under “Natal Day,” Origen, an early Catholic writer, admitted, “…In the Scriptures, no one is recorded to have kept a feast or held a great banquet on his birthday. It is only sinners (like Pharaoh and Herod) who make great rejoicings over the day in which they were born into this world” (emphasis mine).
The Encyclopedia Americana, 1956 edition, adds, “Christmas…was not observed in the first centuries of the Christian church, since the Christian usage in general was to celebrate the death of remarkable persons rather than their birth…a feast was established in memory of this event [Christ's birth] in the fourth century. In the fifth century the Western Church ordered the feast to be celebrated forever on the day of the Mithraic rites of the birth of the sun and at the close of the Saturnalia, as no certain knowledge of the day of Christ's birth existed.”