Why do we celebrate the birth of Christ on December 25th?
Dec. 25 was chosen because the 25th of the 12th month (Chislev) is the first day of the Feast of Dedication (Chanukah) in Israel. The earliest written record of Christians believing that is the correct date goes back to the 2nd century. And no legitimate challenge to the date has ever made sense. Shepherds remain in the fields as far as February in the Holy Land and it almost never gets cold enough to snow in Bethlehem. It's a desert after all. 5BC (the likely correct year of His birth) is interesting as December 25 falls on the same day as Chislev 25 on the Hebrew calendar if you calculate the Western calendar backward.