When a child is conceived, it is the beginning of a new life. This person who never existed before suddenly exists and there is a new person made in the image of God.
This was not the case with Jesus.
When Jesus was conceived, it was not the beginning of his life. The marvel of Christmas is that God the Son, who has existed for all eternity, became a human person.
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. (John 1:1-4 ESV)
The Gospel of John begins by stating that it was through Christ that all creation came into being. Not only is Christmas a time to celebrate the birth of Christ, it is a time to celebrate his eternal glory! It is also a time to think about, with tremendous joy, the future hope we have of living in the presence of Christ in all his glory.