What was the driving force that led the Church to address the heterodox teaching concerning Our Lord's Divine Person?
The perplexing questions that caused this can be boiled down to: how is it that there are two natures in the one Person of Christ? And, just how could there be a union between the two without impairing the character respective to each?
The Church was faced with having to deal with these theological matters head on. One day the doubts surrounded the human nature of Christ, the next day his divine nature. All sorts of pseudo reasoning occurred on the basis of human experience alone, placing human logic above matters of faith. The Church had to face the Nestorians, the Monothelites and the Monophysites and did so through its Ephesine, Chalcedonian and Constantinopolitan Councils and its decrees answering the errors being perpetrated. The Church had to defend itself against the heterodox trends of the day by boldly declaring that God the Word assumed a human nature as a Divine Person, becoming man for the sake of man, and not being created a man. In taking on a human nature, the Second Person of the Trinity was not created a human person because his Person existed from all eternity: In the beginning was the Word, and the Word was with God, and the Word was God," John 1: 1. The human nature assumed, is assumed into the principle reality of God the Word, ever exisitng, without beginning and without end, the Alpha and the Omega.
Therefore, the Divine Person of the Trinity, the Logos, was begotten, not made, and in being begotten was incarnated, that is, took on flesh. The Fathers of the Church at these challenging times in its history clearly defined that the Person of Jesus Christ is a divine Person because from eternity he has existed. In assuming human nature and becoming man, the second Person of the Trinity did not cease to be who he is as the second Person of the Godhead, but assimilated to his Divine Personhood the totality of a human nature; this is what we refer to in theology as the hypostatic union from the Greek, hypostasis, meaning a subsistence of the human nature in the Divine Person, therefore a simultaneous co-existence of the human nature and the divine nature as defined in the orthodox teaching of the First Council of Ephesus in 431 AD, held at the Church of Mary in Ephesus, Asia Minor.
It is by this that the Fathers of the Church countered the heterodox teaching that two natures means two persons, this clearly is not the reality. The Fathers of the Church made it clear that God the Word, as the Second Person of the Holy Trinity, retained his eternal self identity as a Divine Person when assuming a human nature. God, Who became flesh, although fully human at the moment of the incarnation, remained fully divine in the one Divine Person of Jesus Christ, who veiled his divinity in order to experience the totality of our humanity, so as to lift up from the bondage and clutches of sin. Christ God becomes for our human nature the Divine physician and remedy of our souls and bodies.
Through the salvific Christ, the Redemption of man by God becomes a work of man. Through Christ, the union of the human and divine natures in his one Divine Person is the proto-type of what we are all called to: mystical union with God. One may ask, how is it the Christ could understand our humanity as a Divine Person? It is simple. Jesus of Nazareth, fully human, yet fully divine veiled his divinity so as to fully embrace the experience of our humanity. And, because he fully embraced the totality of our human nature He indeed experienced all things like any one of us, except sin. Except sin? Then how can Jesus have understood our fallen human nature if he did not experience sin? Sin is the consequence that entails from our fallen human nature. Even in our human frailty, sin does not exist unless we fall victim to it of our own choosing. Jesus, tempted like us in every way, pride, impure thoughts and unchaste sexual temptations , self aggrandizement, etc. are experiences of our fallen human condition but not sins in and of themselves. Such temptations require an action, a choice.
Jesus chose to keep his heart in communion with the Father. By doing so, he practiced an ascetical existence since he also had to do battle with the same temptations, the same traps that psychologically and spiritually attempt to ensnare us daily. Jesus experienced the totality of our human nature but chose to remain in communion with the Father's Will. Jesus therefore showed us that it is possible to not sin. Yes, it is possible to not sin, but Jesus, in his own aseticism, showed us that it requires constant work and attention.
Jesus' human will was in constant accord with his divine will; this harmony of the human and divine is the destiny of man: union with the will of God through reliance on the Grace of the all holy and life-giving Spirit; it is the mystical marriage of the human with the divine.
In the Person of Our Lord Jesus Christ he eternally is both fully human and fully divine. Our human nature is eternally co-exisitng with his divine nature in the Resurrected and Gloriously Ascended Christ God.