And there were in the same country shepherds abiding in the field... Luke 2:8 [not likely Dec. 25th]
"Today is Christmas day (Christ's mass). But for the first 300 years of Christianity, it wasn't so.
Q: When was Christmas first celebrated? 
A: In an old list of Roman bishops, compiled in A. D. 354 these words appear for A.D. 336: "25 Dec.: natus Christus in Betleem Judeae."
December 25th, Christ born in Bethlehem, Judea. This day, December 25, 336, is the first recorded celebration of Christmas.
For the first three hundred years of the church's existence, birthdays were not given much emphasis--not even the birth of Christ.
Q: How did Christmas come to be celebrated on December 25th?
A: Cultures around the Mediterranean and across Europe observed feasts on or around December 25th, marking the winter solstice.
--The Jews had a festival of lights. 
--Germans had a yule festival.
--Celtic legends connected the solstice with Balder, the Scandinavian sun god who was struck down by a mistletoe arrow.
--At the pagan festival of Saturnalia, Romans feasted and gave gifts to the poor. Drinking was closely connected with these pagan feasts. At some point, a Christian bishop may have adopted the day to keep his people from indulging in the old pagan festival.
Christian stories replaced the heathen tales, but the practices hung on.
--Candles continued to be lit.
--Kissing under the mistletoe remained common in Scandinavian countries.
--But over the years, gift exchanges became connected with the name of St. Nicholas, a real but legendary figure of 4th century Lycia (a province of Asia). A charitable man, he threw gifts into homes.
--Around the thirteenth century, Christians added one of the most pleasant touches of all to Christmas celebration when they began to sing Christmas carols.
No one is sure just when the Christmas tree came into the picture. It 
originated in Germany. The 8th century English missionary, St. Boniface, Apostle to Germany, is supposed to have held up the evergreen as a symbol of the everlasting Christ. ....When the German court came to England, the Christmas tree came with them.
Puritans forbade Christmas, considering it too pagan. Governor Bradford actually threatened New Englanders with work, jail or fines if they were caught observing Christmas.
In 1843, in Victorian England, Charles Dickens published his novelette "A Christmas Carol." It became one of the most popular short works of fiction ever penned....."
Christianity.com