The early Church Fathers often described the nature and purpose of the Church as deification, i.e. to become like God. The Church is the fulfilment of our humanity made in His image and restored in likeness through the action of Christ and the Spirit. But sadly, most Christians in the West have forgotten this. The Eastern Orthodox have tended not to forget what they call theosis, the Greek term for deification. Their theologians have stressed the importance of deification as the purpose of life in Christ. And rightfully so. God became man so that man might become god (notice that I did not capitalize the "g"); obviously, not god by nature but, as St. Peter writes, “participants in the divine nature” (2 Pet. 1:4).
But there's often a prejudice amongst Eastern theologians that this core teaching has been occluded or even not found in the theology of the West. Some claim Christianity in the West has stressed morality more than deification, even though a proper understanding would put them together. They see themselves as heirs of the Greek Church Fathers who they believe, more than the Latin Church Fathers in the West, stressed deification. And St. Augustine of Hippo, unfortunately, gets all the blame for setting Christian theology on the wrong course away from deification.
Thankfully, the Church has scholars like Fr. David Meconi SJ who are setting the record straight. As a Latin Patristics scholar, Most of Fr. Meconi's writings argue that deification is not only at the core of St. Augustine's theology but also found latent within the theology of other Latin Church Fathers. The Church of the West should not be separated from the Church fo the East. It was one Church that was present at the early ecumenical councils in the East. To these councils, we now turn.
The first ecumenical councils were explicitly addressing Christological and thereby Trinitarian heresies, but by implication, they were also addressing deification and salvation, which in the early Church were understood as identical. The Council of Nicea (325) was the first ecumenical council. It was summoned to address the growing threat of Arius’ doctrines.
Arius was a popular priest from Alexandria, an important city in the Roman Empire with a strong Christian intellectual base, famous not only for its library but also its catechetical school. The Alexandrian bishop, Alexander, believed that Arius’ teaching that “there was a time the Son was not” was contrary to the teaching of the Apostles. Arius believed that he was properly interpreting the Scriptures and that he was protecting the transcendence of God. God is eternal and cannot stoop to the level of assuming a human nature, he argued. According to him, the Word that became incarnate in Jesus Christ was the highest creature—but still only a creature and not equal to God. And while humans are joined to this Word, they are never entirely adopted into the divine life of the transcendent God.
Alexander immediately identified the soteriological problem with Arius’ teaching; a young Alexandrian deacon named Athanasius, the future bishop of Alexandria, later developed and risked his life to defend Alexander’s position. Thanks to Athanasius, the Apostolic teaching on deification was preserved and maintained. God became man so that man might become god, as he famously said. Man cannot save himself. Only God can save man, and the most fitting means by which he can do this is by assuming to himself the entirety of human nature. If God did not become man, we are not saved. Man was made to glorify God and the only way into God’s glory is by God taking up our human condition into his glory. Arianism did not allow this, because the mediator was not fully divine and so could not bridge the gap between the human and the divine.
Despite the condemnation of Arianism at Nicea, Arius’ teaching remained a problem within the Church for many years after the council. A few years later, the Council of Constantinople (381) was summoned to address Apollinarianism. Apollinarius taught that Jesus Christ only had a divine mind (nous) and not a human mind. In answer to this heresy, the principle of “what has not been assumed has not been saved” was applied. If Jesus did not have a human mind, then the human mind was not saved. The human being had to be saved in his or her totality and not just in one component of his or her being. During the fourth century, theologians from Cappadocia (smack-dab in the middle of modern-day Turkey) were trying to find ways of preserving the oneness of God while attending to the distinctions within the Godhead that the New Testament introduces. What was the Father, the Son, and the Spirit, anyways? Clearly, the Father was divine but how were the Son and Spirit one in nature with the Father while simultaneously other? To address this question, the Cappodocian Fathers used the term “hypostasis” to talk about the Father, Son, and Spirit. God was three hypostases in one nature.
Later, the Council of Ephesus (431) was called regarding the use of the term “theotokos” (God-bearer) for Mary. Nestorius, the archbishop of Constantinople, had a problem with the use of that term. He was concerned that the language spoke of God in creaturely terms. Nestorius said it would be better to refer to Mary as the bearer of Jesus Christ because he thought that would properly emphasize that Mary gives Jesus his human nature. But at the core of this controversy was a Christological debate. Nestorianism—a view that is probably wrongly attributed to Nestorius— held that Jesus was fully divine and fully human but that there were two separate hypostases— a divine hypostasis for the Son and a human hypostasis for Jesus Christ—and that the two were linked by a noble, moral union. The miracles were to be attributed to the Son, while other “human” activities were attributed to the human person, Jesus Christ. St. Cyril of Alexandria rose up against this position. He obviously acknowledged that Mary did not give birth to God’s eternal nature. No one held that position. But he defended the teaching that, in the case of Christ, there is only one hypostasis that unites his divine and human natures. Since Jesus is only one hypostasis, or person (i.e., the divine person of the Son)—and mothers give birth to persons, not just natures—it was proper to speak of Mary as “Mother of God." But there was still confusion within the Church about the identity of Jesus Christ.
The language of hypostasis and nature was further refined and clarified at the Council of Chalcedon in 451, and came to be referred to, in later theology, as the “hypostatic union.” It is worth knowing the Chalcedonian definition if ask about the identity of Christ. It states:
Therefore, following the holy fathers, we all unite in teaching that we should confess one and the same Son, our Lord Jesus Christ. This same one is perfect in deity, and the same one is perfect in humanity; the same one is true God and true man, comprising a rational soul and a body. He is of the same essence (homousios) as the Father according to his deity, and the same one is of the same essence (homousios) with us according to his humanity, like us in all things except sin. He was begotten before the ages from the Father according to his deity, but in the last days for us and our salvation, the same one was born of the Virgin Mary, the bearer of God (Theotokos), according to his humanity. He is one and the same Christ, Son, Lord, and Only Begotten, who is made known in two natures (physeis) united unconfusedly, unchangeably, indivisibly, inseparably. The distinction between the natures (physeis) is not at all destroyed because of the union, but rather the property of each nature (physis) is preserved and concurs together into one person (prosopon) and subsistence (hypostasis). He is not separated or divided into two persons (prosopa), but he is one and the same Son, the Only Begotten, God the Logos, the Lord Jesus Christ. This is the way the prophets spoke of him from the beginning, and Jesus Christ himself instructed us, and the Council of the fathers has handed the faith down to us.
The first 500 years of the Church are important in resolving the Christological and Trinitarian controversies and better establishing the teachings of the Church. And a key implication of affirming Christ’s full divinity and full humanity was the protection of the belief in deification since our nature had been drawn, in Christ, into union with the divine nature.