St. Ephraim the Syrian: A Confession of the God-Man Jesus Christ

 A Confession of the God 

Who became man in Jesus Christ the Lord

He Who is from God, God the Word, the only-begotten Son of the Father, of one essence with the Father, Being from Being, ineffably begotten of the Father without a mother before all ages - the very same is born in the last days to a daughter of men, to the Virgin Mary without a father. God is born incarnate, wearing flesh borrowed from her, having become man, which He was not, and remaining God, which He was, in order to save the world. And He is Christ, the Son of God, the only-begotten of the Father and the only-begotten of His Mother.

I confess One and the Same as both perfect God and perfect Man, in two natures, united in one hypostasis or person, recognized as indivisible, unconfused and unchangeably God Who was clothed in flesh, animated by an intelligent and rational soul, and came to resemble us in every way except sin.

One and the Same is earthly and heavenly, temporal and eternal, both with and without beginning, timeless and subject to time, created and uncreated, suffering and free from suffering, God and Man and perfect in both. One in two natures, in both Unitary.

+St. Ephraim the Syrian, quoted by St. Theophan the Recluse in A Spiritual Psalter: or Reflections on God, psalm 29.

St. Leo the Great: On the two natures of Christ

 The properties of the two natures (divine and human) thus remain entire but come together in one Person: majesty is bound to humility, power to weakness, eternity to mortality. In order to be able to pay off the debt belonging to our condition, the nature inaccessible to suffering is united to that which can suffer and, as was needful in order to save us, Jesus Christ made man, the one and the same Mediator between God and man, could die in his human nature while remaining immortal in his divine nature... He has taken the form of a slave without the stain of sin, raising up humanity, without detracting from the Godhead. For this abasement, whereby the Invisible is made visible, and the Creator, the Lord of all things, have wished to become one of those subject to death, has been a condescension of His mercy, not a diminution of His power... So the Son of God has come into this world, descending from His abode in heaven but without giving up the glory of His Father; and He is born into a new order of things and by a new birth... The same Person is thus at once true God and true man; and this unity is genuine, for it comprises the humanity of man and the majesty of God... The Catholic Church lives and ever continues by this faith that, in Jesus Christ, neither the manhood without the true Godhead nor the Godhead without the true manhood is believed in.

+St. Leo the Great, from Letter 28 to St. Flavian¹, in Leo the Great Collection.
¹This letter is that which was read at the 4th Ecumenical Council in Chalcedon in 451AD.