It happened some 2000 years ago, it was written a half century or so later, and it was quoted famously in 1965:
“8And there were in the same country shepherds abiding in the field, keeping watch over their flock by night.
9And, lo, the angel of the Lord came upon them, and the glory of the Lord shone round about them: and they were sore afraid.
10And the angel said unto them, Fear not; for, behold, I bring you tidings of great joy, which shall be to all people.
11For unto you is born this day in the city of David a Savior, which is Christ the Lord.
12And this shall be a sign unto you: Ye shall find the babe wrapped in swaddling clothes, lying in a manger.
13And suddenly there was with the angel a multitude of the heavenly host praising God, and saying,
14Glory to God in the highest, and on earth peace and goodwill towards men.” (Luke -KJV).
“…That’s what Christmas is all about, Charlie Brown.”(Mendelson)
What could I possibly add to that?