Read other letters about this article
There is no scriptural basis for placing the celebration of Christ's birth in December (in fact, it probably occurred in the spring); the reasons, rather, are astronomical/theological.
December 25 is just about at the Winter Solstice, when the days start to get long again (i.e., the duration of daylight begins to increase). Since Christ is the "light of the world," this increase of light corresponds to the Christ's "light" coming into the world.
Similarly, Easter occurs at about the Spring Equinox each year, when the amount of daylight becomes greater than the amount of nighttime (i.e., the light overcomes the darkness, a parallel to the theological understanding of Christ's death and resurrection).
That's why the early Christians appropriated the celebrations held at those times, and used their symbolism to make theological statements about Christ.