The Son of God did exist with God the Father at the creation of the world as evidenced by many passages of Scripture, including this one from Colossians . 1:15_20

"He is the image of the invisible God, the firstborn over all creation. For by him all things were created: things in heaven and on earth, visible and invisible, whether thrones or powers or rulers or authorities; all things were created by him and for him. He is before all things, and in him all things hold together. And he is the head of the body, the church; he is the beginning and the firstborn from among the dead, so that in everything he might have the supremacy. For God was pleased to have all his fullness dwell in him, and through him to reconcile to himself all things, whether things on earth or things in heaven, by making peace through his blood, shed on the cross."

We learn a lot about the Son of God from that passage. We learn that he truly did exist at creation, and in fact, was active in that creation. We also learn that he is fully God and that his sacrifice on the cross made peace between a sinful humanity and a sinless God.

John chapter tells us some of the same things when it says:

• "In the beginning was the Word, and the Word was with God, and the Word was God.
• He was with God in the beginning.
• Through him all things were made; without him nothing was made that has been made....
• He was in the world, and though the world was made through him, the world did not recognize him....

But a few verses later John also adds the fact that the Son of God came to earth as Jesus when he tells us: 

• "The Word became flesh and made his dwelling among us. We have seen his glory, the glory of the One and Only, who came from the Father, full of grace and truth."

The Apostle Paul shares the same truth in Philippians chapter 2:

• Your attitude should be the same as that of Christ Jesus:  Who, being in very nature God, did not consider equality with God something to be grasped, but made himself nothing, taking the very nature of a servant, being made in human likeness.  And being found in appearance as a man, he humbled himself and became obedient to death– even death on a cross!

The Son of God existed in eternity before the creation of the world, but at just the right time (see Galatians 4:4) God sent his Son into the world as the baby Jesus - fully human and yet fully God - who would grow up to take the punishment for the sins of mankind, so that we might be offered forgiveness and eternal life.

The mystery of God becoming man in order to bring man back to God is what we celebrate at Christmas!