When discussing the topic of the dual natures of Christ from an Orthodox perspective, the first place we can begin is with the confession of St. Peter, “He said to them, ‘But who do you say that I am?’ Simon Peter replied, ‘You are the Christ, the Son of the living God.’ And Jesus answered him, ‘Blessed are you, Simon Bar-Jona! For flesh and blood has not revealed this to you, but my Father who is in heaven.’” (Matthew 16:15-17) To come to the full understanding of Jesus Christ as being both fully God and fully man is only possible by Divine Revelation, given by the Father, in the Son, through the Holy Spirit; it is not a matter of rational speculation, for the union between God and man is a mystery beyond comprehension.
The first point of Christology is to confess the full Divinity of the Christ; Jesus Christ is fully God. He is the Pre-Existent Word (Logos) of the Father, eternally begotten, the Second Person of the Trinity, Who’s Divinity is constantly expressed throughout the Scriptures (Mark 1:1, John 20:31, Matthew 3:17, Matthew 16:16, 1 John 5:20, Colossians 2:9, etc..) and is clearly stated within the Nicene-Constantinopolitan Creed, “And in one Lord Jesus Christ, the only-begotten Son of God, begotten of the Father before all worlds; God of God, Light of Light, very God of very God; begotten, not made, being of one substance with the Father, by whom all things were made.” The second is to also confess the He was fully man, as is expressed in the rest of the clause in the Creed which is devoted to the Son, “Who, for us men for our salvation, came down from heaven, and was incarnate by the Holy Spirit of the virgin Mary, and was made man; and was crucified also for us under Pontius Pilate; He suffered and was buried; and the third day He rose again, according to the Scriptures; and ascended into heaven, and sits on the right hand of the Father; and He shall come again, with glory, to judge the quick and the dead; whose kingdom shall have no end.” He was born of the Virgin Mary, possessing a human mind, soul, will, activity, and body; fully experiencing the human condition, apart from sin (both ancestral and voluntary) ; He hungered, thirsted, grew weary, slept, wept, suffered, and died.
In regards to the manner of the union between the Divinity and Humanity of Christ the Orthodox Church confesses that the Divine and Human natures are perfectly united to one another in His Divine Personhood; He is ‘One Person in Two Natures’, with His Human nature being entirely subject to, and in harmony with, the Divine. One of the clearest statements regarding the mystery of Christ is found in the declaration of the Council of Chalcedon, “Following the Holy Fathers we teach with one voice that the Son and Our Lord Jesus Christ is to be confessed as one and the same [Person], that He is perfect in Godhead and perfect in manhood, very God and very man, of a reasonable soul and [human] body, one in Essence with the Father as touching His Godhead, and one in essence with us as touching His manhood; made in all things like unto us, as touching sin only excepted; begotten of His Father before the world according to His Godhead, but in the last days for us men and for our salvation born of the Virgin Mary the Theotokos, according to His manhood. This one and the same Jesus Christ, the only begotten Son, must be confessed to be in two natures, unconfusedly, immutably, indivisibly, inseparably…not separated or divided into persons, but one and the same Son and only-begotten God the Word, Our Lord Jesus Christ, as the prophets of old time have spoken concerning Him, and as the Lord Jesus Christ hath taught us, and as the Creed [The Nicene-Constantinopolitan] of the Fathers hath delivered us.”
Though the two natures are united they remain distinct, neither of them being absorbed into the other. There is never a moment when the natures are divided either; the Word of God took on, and united Himself to, human nature from the womb of the Theotokos, and this union is permanent. Through the union to the Divine Nature in the Person of the Word of God – the ‘hypostatic union’ – entered also into an ‘energetic union’; the human nature was enriched with, and participated in, the Divine Energies (not the Divine nature) while still retaining it’s own attributes and nature, as well as the human will remained whole and operative while being united, and subjected in harmony, to the Divine will – the one will common to the Holy Trinity (since the will is a property of ‘nature’ rather than of ‘person’, the Trinity possesses one Divine Will). The Fathers likened the union of the two natures, while still remaining distinct (as well they understood the deification of the human by the divine in this same matter), to a blade being heated, “the steel which has been heated burns, not because it has a naturally acquired powering of burning, but because it has acquired it from it’s union with fire.” (St. John of Damascus)