A pagan holiday of the winter solstice (Dec. 25) designated to worship Isis and her baby son was adopted by the Constantine as a christian holiday to unite the people who were different on religion.
With the general conversion of Europe to Christianity, the date was linked to the birth of Jesus, but there is no clear scriptural support for that particular date.
The ancient Romans celebrated the Winter Solstice on this day in honor of the "Unconqured Sun". In addition, a very popular Mystery Cult devoted to the Persian god Mithras also honored him that day. Christianity, a syncretistic religion, adopted this day as the celebration of Christ's birth much like it did with Samhain and the festival of Pomona for All Saints Day (Halloween).
So let's look at the scriptures.
Hear what the Lord says to you, O house of Israel. This is what the Lord says: "Do not learn the ways of the nations or be terrified by signs in the sky, though the nations are terrified by them.
For the customs of the peoples are worthless; they cut a tree out of the forest, and a craftsman shapes it with his chisel. They adorn it with silver and gold; they fasten it with hammer and nails so it will not totter."
Jeremiah 10:1-4
