The doctrine of the Theanthropos was hammered out on the anvil of controversy, and the church’s confession at Chalcedon stands as a fourfold fence against the heresies that assailed the person of Christ. Arianism denied His true deity, making Him the highest creature—but a creature cannot be God-man. Apollinarianism denied His full humanity, teaching that the divine Logos replaced the human soul, leaving Christ with a human body but not a human mind—but what is not assumed is not healed, and a Savior lacking a human soul could not redeem the soul. Nestorianism so divided the natures as to make two persons loosely joined—but then the deeds of the man are not the deeds of God, and the Lord of glory was not crucified. Eutychianism (monophysitism) confused the two natures into one, the human absorbed into the divine like a drop in the ocean—but then Christ is neither truly God nor truly man, but a third thing, and no real mediator.

Against all four, Chalcedon confessed Christ to be truly God and truly man, made known in two natures ‘without confusion, without change, without division, without separation,’ the distinction of natures preserved and concurring in one person. This is no mere philosophical nicety but the very ground of salvation, for the necessity of the God-man arises from the work He came to do. Only one who is truly God could give His obedience and suffering infinite value, bear the full weight of divine wrath, and conquer death; only one who is truly man could represent men, keep the law in their nature, and die in their place. Diminish His deity, and His sacrifice cannot save; diminish His humanity, and He cannot stand for us; divide or confuse the natures, and there is no Mediator at all. The whole gospel rests on the wonder confessed in the Theanthropos: that in one person, God and man are joined, that God and man might be reconciled.