People of God, Christmas can be summarized by that phrase in verse 37: For nothing is impossible with God. How can a virgin conceive? How can a barren woman in her old age conceive? This is all a part of this great cosmic plan of redemption. At a time when there is no hope, no salvation and deliverance, and when the world is most overtaken by sin and misery, it is then when we must remember: Nothing is impossible with God.
But the greatest of all impossibilities is the Coming of God to His own creation in the Lord Jesus Christ. As Mary became the servant of the Lord, the Son she would bear becomes the servant of all. In the incarnation, the eternal Son of God takes the form of the servant as a man, but also giving Himself up to man’s rebellion against God, placing Himself under the judgment under which man has fallen in this rebellion, under the curse of death which rests upon Him.
“He makes his own the being of man under the curse, but in order to do away with it. He acts as Lord over this rebellion even as He subjects Himself to it. He frees the creature in becoming a creature. He overcomes the flesh in becoming flesh.”  He reconciles the world by serving the world.
But how can the victorious Lord become an obedient servant without betraying His lordship? Paradoxical as it may sound; we must embrace this truth of Christmas, this fundamental truth of the gospel: that it is in the nature of the God/Man to be a servant to His Creation.
The Son does not need to leave the work of reconciliation in sinful hands for He himself enters this world and reconciles us in His service and obedience. Christ, the Second Person of the Trinity, born of a virgin, becomes like us, so He can save us in His death, burial, and resurrection. The paradox of Christmas is answered once again in this phrase: Nothing is impossible with God.
 Some thoughts from Leithart, though I have taken a different angle.