In the beginning was the Word, and the Word was with God, and the Word was God. He was in the beginning with God. All things were made through him, and without him was not any thing made that was made. In him was life, and the life was the light of men. The light shines in the darkness, and the darkness has not overcome it. . . . The true light, which enlightens everyone, was coming into the world. He was in the world, and the world was made through him, yet the world did not know him. He came to his own, and his own people did not receive him. But to all who did receive him, who believed in his name, he gave the right to become children of God, who were born, not of blood nor of the will of the flesh nor of the will of man, but of God.
And the Word became flesh and dwelt among us, and we have seen his glory, glory as of the only Son from the Father, full of grace and truth. (John bore witness about him, and cried out, "This was he of whom I said, 'He who comes after me ranks before me, because he was before me.'") And from his fullness we have all received, grace upon grace. For the law was given through Moses; grace and truth came through Jesus Christ. No one has ever seen God; the only God, who is at the Father’s side, he has made him known. - John 1:1-5; 9-18 (ESV)
Christmas is a celebration of Christ, The Word, who was made flesh. This incarnation (God becoming man) is the center of this festival and apart from this miracle, there would be no salvation for any man; all have sinned against God and deserve his just and holy wrath. Praise be to God that he saw fit to send his Son, Jesus Christ, to die for my sins.