As an explanation of why we celebrate Christmas each year, the below video is superb and concise.
The words of Linus are of course taken from the Gospel of Saint Luke:
And there were in the same country shepherds abiding in the field, keeping watch over their flock by night.
And, lo, the angel of the Lord came upon them, and the glory of the Lord shone round about them: and they were sore afraid.
And the angel said unto them,
Fear not: for, behold, I bring you good tidings of great joy, which shall be to all people.
For unto you is born this day in the city of David a Saviour, which is Christ the Lord.
And this shall be a sign unto you; Ye shall find the babe wrapped in swaddling clothes, lying in a manger.
And suddenly there was with the angel a multitude of the heavenly host praising God, and saying,
Glory to God in the highest, and on earth peace, good will toward men.
When I was a boy the Charlie Brown Christmas Special was my favorite TV Christmas Special. As a man, I agree.