At the root of most heresy is the question of the character of Christ. Most heresy in some way perverts the Biblical teaching on who Christ is or the nature of His work in redemption. In the fifth century AD it became necessary for the church to deal with two heresies concerning the nature of Christ; the Nestorian Heresy and the Monophysite Heresy.
Nestorius taught that Christ was two beings, one human and one divine, sharing the same body. The First Council of Ephesus (431) dealt with this heresy, labeling it as such and excommunicating Nestorius. The ink had not yet dried on the documents from Ephesus before the opposite teaching reared its ugly head. The Monophysite heresy, taught chiefly by Eutychius, stated that Christ was indeed a single being with two natures, human and divine. The problem was that Eutychius taught that the human nature was enclosed, or absorbed by the divine nature.
Though Eutychius was excommunicated at a synod in Constantinople, the Emperor Theodosius II, and the Archbishop of Alexandria, Dioscurus I, revived the Monophysite Heresy, declaring Eutychius and his views orthodox. Immediately, attempts to bring the church together to put this issue to rest once and for all began. The Providential death of Theodosius removed the one obstacle blocking what became known as the Council of Chalcedon.
For nearly a month some 500 bishops from all parts of Christendom deliberated over the documents from earlier church councils and synods in the light of scripture because,
“the evil one never stops trying to smother the seeds of religion with his own tares and is for ever inventing some novelty or other against the truth; so the Master, exercising his usual care for the human race, roused this religious and most faithful emperor to zealous action, and summoned to himself the leaders of the priesthood from everywhere, so that through the working of the grace of Christ, the master of all of us, every injurious falsehood might be staved off from the sheep of Christ and they might be fattened on fresh growths of the truth.”
The Council of Chalcedon thoroughly repudiated both the Nestorian and Monophysite Heresies. They bequeathed to the church for all ages the definition of Christ's character as one person with two natures; fully human, fully divine, “which undergo no confusion, no change, no division, no separation...”
Theologians to this day return to Chalcedon to understand the difficult doctrines of the dual nature of Christ. It is difficult for the human mind to comprehend an inseparable human and divine nature in one person. The bishops of the Council of Chalcedon have simply stated the Biblical teachings of this doctrine. It is for the Christian to believe the teaching of scripture even when we cannot understand how it works.