To Flavianus, Bishop of Constantinople.
I have already in another letter informed your holiness how openly the calumniators of our teaching are slandering us. Now in like manner by means of the very godly bishops I do the same, having not only these as witnesses of the orthodoxy of my teaching but also countless other men who are my hearers in the churches of the East. Above and beyond all these I have my conscience, and Him who sees my conscience. And I know too how the divine Apostle often appealed to the testimony of his conscience, for
our rejoicing is this, the testimony of our conscience and again
I say the truth in Christ I lie not, my conscience also bearing me witness in the Holy Ghost. Know then, O holy and godly sir, that no one has ever at any time heard us preaching two sons; in fact this doctrine seems to me abominable and impious, for there is one Lord Jesus Christ through whom are all things. Him I acknowledge both as everlasting God and as man in the end of days, and I give Him one worship as only begotten. I have learned however the distinction between flesh and Godhead, for the union is unconfounded. Thus drawn up as it were in battle array to oppose the madness of Arius and Eunomius, we very easily refute the blasphemy hazarded by them against the only begotten, by applying what was spoken in humility about the Lord, and suitably to His assumed nature, to man, and, on the other hand, what becomes the divine and signifies the divine nature, to God; not dividing Him into two persons, but teaching that both the former and latter attributes belong to the only begotten, the latter to Him as God the Creator and Lord of all, and the former as made man on our account. For divine Scripture says that He was made man, not by mutation of the Godhead, but by assumption of human nature, of the seed of Abraham. This the divine Apostle openly says in the words
For verily He took not on Him the nature of angels, but He took on Him the seed of Abraham, wherefore in all things it behooved Him to be made like His brethren. And again
These and similar passages have been cut out of divine Scripture by Simon, Basilides, Valentinus, Bardesanes, Marcion, and the man who is named after his maniacal heresy. So they style the Master Christ God only, and describe Him as having nothing human about Him, but appearing in imagination and appearance as man to men. On the other hand the Arians and Eunomians say that God the Word assumed only a body, and that He Himself supplied the place of a soul in the body. And Apollinarius describes the Master's body as endued with a soul; but, deriving, I know not whence, the idea of a distinction between soul and intelligence, deprives intelligence of its share in the achieved salvation. The teaching of the divine Apostles lays down on the contrary that a soul both reasonable and intelligent was assumed together with flesh, and the salvation of which the hope is held out to them that believe is complete.
There is yet another gang of heretics who hold differently. Photinus, Marcellus, and Paul of Samosata, assert that our Lord and God was only man. When arguing with these we are under the necessity of advancing proofs of the Godhead, and of showing that the Master Christ is everlasting God. When, on the other hand, we are contending with the former faction, which calls our Lord Jesus Christ God only, we are obliged to marshal against them the forces of the divine Scripture, and collect from it evidence of the assumption of the manhood. For a physician must use remedies appropriate to the disease, and suit the medicine to the case.
Now, therefore, I beseech your holiness to scatter the slander raised against me, and bridle the tongues now vainly reviling me. For, after the incarnation, I worship one Son of God, one Lord Jesus Christ, and denounce as impious all who hold otherwise. Deign, sir, to give me too your holy prayers, that, by God's grace, I may reach the other side of the ocean of danger, and drop my anchor in the windless haven of the Lord.
Source. Translated by Blomfield Jackson. From Nicene and Post-Nicene Fathers, Second Series, Vol. 3. Edited by Philip Schaff and Henry Wace. (Buffalo, NY: Christian Literature Publishing Co., 1892.) Revised and edited for New Advent by Kevin Knight. <http://www.newadvent.org/fathers/2707104.htm>.