In order for God the Son to fulfill the role of Christ, he had to become a man. So, he became incarnate as Jesus. As a result, Jesus was both man and God — one person with two natures in hypostatic union. He had all the essential attributes of a human being, and all the essential attributes of deity. But these realities can seem hard to reconcile.
When we speak about Jesus as the God-man, the term that the church coined to discuss that was “hypostatic union,” meaning that there is a coming together of natures, the divine nature and the human nature, that in Jesus Christ we have one person, God the Son, the second person of the Trinity. One person, who brings two natures together, and makes them united, doesn’t make a third nature out of them. Instead he unites the divine and the human.
Now, while that is a very difficult concept for us to wrap our minds around, it is utterly essential for our faith — understanding the absolute uniqueness of Jesus. He is the God-man. He’s not just a great, exalted, enlightened teacher, such as the prophet Buddha or the prophet Mohammed. No, Jesus is the God-man. So his identity is caught up in this notion of the hypostatic union. But beyond that, there is also something crucial for us in understanding our salvation in Christ. Christ does not come simply to pay a debt that we owe to God, so that God can write our debt off the books. No, Christ comes to bring us back to the Father.
Christ comes to unite the divine life that is lost in the fall of Adam, back to our humanity. Only if Christ is the one who can bring God and man together can we really say that we have been saved. Not just forgiven of our sins, but saved, made again what God intended us to be all along, those who bear his image, those who live in the fullness of his presence, and those whose lives are united to him in love, faith and obedience. So, the doctrine of the hypostatic union, as hard as it is, is absolutely essential for us to keep in mind, and always thinking about because of the identity of Jesus on the one hand, and on the other hand his identity as the one and the only one who can bring us back to God. Not by what he did on the cross, but because of who he is in his very nature, the God-man.
The question of what is the nature or the natures of Christ in the hypostatic union is one of the more difficult questions in theology, and the reason for this is we’re seeking to understand a mystery. The nature has to do with Christ’s humanity and his deity, and he had both a human nature and a divine nature. And what is interesting in the way the Scripture presents is that these are not blends; he is fully human and he is fully divine, and they do not come together in a confused manner, but Christ at the same time was both human and divine.
The term “hypostatic union” itself often sounds confusing, and then when you hear it explained that we’re talking about divine nature of the second person of the Trinity, united with a full and complete human nature, sinless human nature, but full and complete — body, soul, mind the whole works — in one person, that concept in itself, as well as the term, is amazing, especially in the light of the fact that Scripture so often emphasises in the Old Testament that we should not confuse God and man.
Yes, man is made in God’s image and God’s likeness, but we shouldn’t confuse the Creator and the creature. And here in the New Testament we find this very clear announcement that in Jesus Christ we need one who is obviously fully human, exhausted to the point of sleep in the midst of a storm on the Sea of Galilee and at the same time fully God, so that when roused from that sleep, as the Creator of the universe, he ushers the word “silence,” and the whole storm stops in obedience to its Creator. So there’s a text right there that puts the hypostatic union right before us and demands that we, if we hear the Word of God, that we accept it.
The hypostatic union, this idea that in Christ we have a fully divine nature and a fully human nature coming together in one person, this is what enables God to show himself to us and to redeem us as only Christ is able to do. We have one mediator between God and man, the man Christ Jesus, and it’s essential that he’s both God and man to be this mediator.