Leo, bishop, to the most beloved brother Flavian, bishop of Constantinople.

Chapter I: Eutyches’s Ignorance of Scripture Led Him into Heresy

Having read your beloved’s letters, which We marvel arrived so late, and having reviewed the account of the episcopal proceedings, We have at last come to understand the scandal against the integrity of the faith that has arisen among you. What had seemed hidden is now plain. Eutyches, held in some honor by reason of his presbyter’s title, has been shown to be entirely imprudent and unskillful, as the prophet says of such a man: He refused to understand that he might do good; he devised iniquity upon his bed (Ps. 35:4).

What is more unjust than to hold impious views and refuse to yield to those wiser and more learned? Into this folly fall those who, unable to arrive at the truth through some obscurity, turn not to the voices of the prophets, the letters of the apostles, or the authorities of the Gospels but to themselves — becoming teachers of error because they refused to be disciples of truth. What learning has Eutyches gathered from the sacred pages of the Old and New Testaments, unable even to grasp the most elementary declaration of the Creed? The heart of this old man has not yet come to hold what the entire reborn world professes.

Chapter II: Against Those Who Divide Christ’s Dispensation into Two Sons; The Eternal Generation of the Son and the Temporal Birth from the Virgin

Ignorant of what to think about the Incarnation of the Word of God, and unwilling to labor through the breadth of the Scriptures for understanding’s light, Eutyches should at least have received with care that common and undivided confession of the whole body of the faithful: I believe in God the Father almighty, and in Jesus Christ His only Son, our Lord, born of the Holy Spirit and the Virgin Mary. These three clauses overthrow nearly all heretics’ devices.

For when God is believed to be both almighty and Father, the Son is shown to be coeternal with Him, differing in nothing from the Father: God from God, almighty from almighty, coeternal from eternal — not later in time, lesser in power, unlike in glory, or divided in essence. The same eternal only-begotten Son of the eternal Father was born of the Holy Spirit and the Virgin Mary. This birth in time took nothing away from and added nothing to that divine eternal birth; its purpose was wholly devoted to the restoration of man who had been deceived — to overcome death and, through His power, to destroy the devil who held dominion over death.

We could not overcome sin and the author of death unless He took our nature and made it His own — He whom sin could not defile nor death detain. He was conceived of the Holy Spirit within the womb of the Virgin, who bore Him with virginity intact as she had conceived Him without violation. But if Eutyches was unable to draw a pure understanding from this purest source of the Christian faith, darkened as he was by his own blindness, he should have submitted himself to the teaching of the Gospels.

Matthew says: The book of the generation of Jesus Christ, the son of David, the son of Abraham (Matt. 1:1). He should have sought the instruction of the Apostle, and read in the letter to the Romans: Paul, a servant of Jesus Christ, called to be an apostle, set apart for the Gospel of God, which He promised beforehand through His prophets in the holy Scriptures, concerning His Son, who was made for Him from the seed of David according to the flesh (Rom. 1:1–3). With pious care he should have turned to the prophetic pages, where God says to Abraham: In your seed shall all nations be blessed (Gen. 22:18). To avoid any uncertainty about the nature of this seed, he should have followed the Apostle: To Abraham and his seed were the promises made. It does not say “and to his seeds,” as of many, but as of one, “and to your seed,” which is Christ (Gal. 3:16). He should have grasped inwardly Isaiah’s prophecy: Behold, a virgin shall conceive and bear a son, and they shall call His name Emmanuel, which means God with us (Isa. 7:14; Matt. 1:23). He should have read with faith: A child is born to us, a son is given to us, whose government is upon His shoulder, and they shall call His name Angel of Great Counsel, Wonderful, Counselor, Mighty God, Eternal Father, Prince of Peace (Isa. 9:6).

Not speaking idly, he should not have said that the Word becoming flesh meant that Christ, born from the Virgin’s womb, had a human form without the reality of her body. Or did he perhaps think that our Lord Jesus Christ was not of our nature simply because the angel said to the blessed ever-virgin Mary: The Holy Spirit will come upon you, and the power of the Most High will overshadow you; therefore the holy one born of you will be called the Son of God (Luke 1:35)? The divine and singular manner of His conception does not mean that His flesh was not of the nature of her who bore Him. This unique manner of birth was to be rightly understood, not misconstrued.

Chapter III: Against Those Who Assert the Son’s Divinity Is Passible; The Two Natures and One Person of Christ

With the properties of each nature and substance preserved, and coming together into one person, majesty assumed humility, strength assumed weakness, eternity assumed mortality. To pay the debt that belonged to our condition, inviolable nature united with passible nature — so that, as suited our healing, one and the same mediator of God and men, the man Jesus Christ (1 Tim. 2:5), could die in respect of the one and not die in respect of the other. In the whole and perfect nature of true man, therefore, true God was born — wholly in what was His, wholly in what was ours. What was ours was what the Creator fashioned in us from the beginning and undertook to restore. The additions of the deceiver and what man admitted by transgression left no trace in the Savior. Though He took on human infirmities, He did not assume our sins. He took the form of a servant without the defilement of sin, enhancing what was human while not diminishing what was divine. That “self-emptying” by which the Invisible made Himself visible, and the Creator and Lord of all things willed to be one among mortals, was a condescension of mercy, not a failure of power.

Accordingly, the one who, remaining in the form of God, made man, was made man in the form of a servant. Each nature retains its proper character without defect: as God’s form does not take away the servant’s form, so the servant’s form does not diminish God’s form. Because the devil was boasting that man, deceived by his fraud, had been stripped of divine gifts and, bereft of his endowment of immortality, had incurred the harsh sentence of death — and that in his shared ruin the deceiver himself had found some consolation — and because God, moved by the demands of justice, had changed His purpose toward man, whom He had created in such honor: God’s eternal and unchangeable will required that the secret counsel of an inscrutable dispensation should be fulfilled, so that man, led astray by diabolic cunning, should not perish against God’s design.

Chapter IV: Against Those Who Claim Christ’s Natures Are Mixed or Confused; The Two Natures Act in Communion

The Son of God entered these lower regions of the world, descending from His heavenly throne yet not departing from the Father’s glory, born in a new order, by a new kind of birth. In a new order: because He who is invisible in what is His became visible in what is ours; He who could not be comprehended willed to be comprehended; He who, being before time, began to exist in time; the Lord of all things took the form of a servant, veiling the immensity of His majesty; God impassible did not disdain to become man passible, and the immortal did not refuse the laws of death. By a new kind of birth: because inviolate virginity, knowing no concupiscence, supplied the matter of the flesh. What was taken from the Mother was nature, not fault. In the Lord Jesus Christ, born of the Virgin’s womb, His marvelous birth does not make His nature different from ours. For He who is true God is likewise true man — there is no falsehood in this unity — as human lowliness and divine loftiness meet together. As God is not changed by the mercy He shows, so man is not consumed by the dignity he receives.

Each form acts in communion with the other, doing what belongs to it:1 the Word performing what belongs to the Word, and the flesh fulfilling what belongs to the flesh. The one shines with miracles, the other submits to injuries. The Word does not withdraw from equality with the Father in His glory; the flesh does not abandon the nature of our race.

One and the same — and this must be said again and again — is truly the Son of God and truly the son of man. He is God, as it is written: In the beginning was the Word, and the Word was with God, and the Word was God (John 1:1); He is man, as it is written: the Word was made flesh and dwelt among us (John 1:14). He is God, as it is written: all things were made through Him, and without Him was nothing made (John 1:3); He is man, as it is written: born of woman, born under the law (Gal. 4:4). The birth of the flesh is a manifestation of human nature; the Virgin’s delivery is a sign of divine power. The infancy of the child is shown by the lowliness of the cradle; the greatness of the Most High is proclaimed by the voices of angels (Luke 2:14). He is like human infants whom Herod wickedly seeks to destroy (Matt. 2:16); He is the Lord of all whom the Magi are eager to adore in joyful prostration (Matt. 2:11). When He comes to the baptism of John, lest His divinity remain hidden under the veil of the flesh, the Father’s voice from heaven thunders: This is my beloved Son, in whom I am well pleased (Matt. 3:17). The devil tempts Him as a man (Matt. 4:1); the angels minister to Him as God (Matt. 4:11). To hunger and thirst and tire and sleep is manifestly human; to satisfy five thousand with five loaves (John 6:10), to give the Samaritan woman living water (John 4:10), to walk with unfaltering tread upon the surface of the sea (Matt. 14:25), to calm the raging waves by a word of rebuke (Luke 8:24) — this is undoubtedly divine. To weep from genuine human compassion over a dead friend (John 11:35); to call him forth from the tomb after four days by the power of a command (John 11:43); to hang upon the cross and make the elements tremble and the light fail; to be pierced with nails and open the gates of paradise to the faith of the thief (Luke 23:43) — this belongs to neither nature alone, but to the one and same person. To say I and the Father are one (John 10:30), and to say the Father is greater than I (John 14:28): though one person is Lord Jesus Christ, both are stated truly, because His humanity is less than the Father, while His divinity is equal to the Father.

Chapter V: Against Those Who Assert the Form of the Servant Is Heavenly or of Another Substance; The Truth of the Resurrection Body

For this unity of person in both natures, it is said that the Son of Man descended from heaven, when the Son of God took flesh from the Virgin (John 3:13); and again, the Son of God is said to have been crucified and buried, when He endured this not in His divinity by which He is coeternal and consubstantial with the Father, but in the weakness of His human nature. Thus we all confess in the Creed that the only-begotten Son of God was crucified and buried, according to what the Apostle says: For if they had known, they would never have crucified the Lord of glory (1 Cor. 2:8).

When our Lord and Savior was instructing His disciples’ faith, He asked: Who do men say that the Son of Man is? When He had heard the various opinions of others, He said: But who do you say that I am? — that is: “I who am the Son of Man, in the form of a servant and in the truth of the flesh, who do you say I am?” Whereupon the blessed Peter, by a divine inspiration that would benefit all nations, replied: You are the Christ, the Son of the living God (Matt. 16:16). And not without reason was he declared blessed by the Lord, drawing from the chief rock both his strength and his name,2 when by the Father’s revelation he had confessed both the Son of God and the Christ. Receiving one without the other is of no advantage for salvation: it is equally dangerous to have believed the Lord Jesus Christ to be only God without man, or only man without God.

After the Lord’s resurrection — a resurrection of a real body, since none other rose than the one who had been crucified and had died — the whole purpose of the forty days before the Ascension was to cleanse the eyes of our heart from every cloud of obscurity, so that faith might rest on a purified foundation. Conversing with His disciples, eating with them, allowing Himself to be handled with close and careful examination by those who were gripped by doubt (Luke 24:38); entering among them with shut doors (John 20:19); breathing upon them the Holy Spirit (John 20:22); enlightening their minds by opening the Scriptures (Luke 24:45); showing the wound in His side, the marks of the nails, and all the signs of His recent Passion — He said: See my hands and my feet, that it is I myself. Touch me and see, for a spirit has not flesh and bones as you see I have (Luke 24:39). All this was intended to show that the divine nature and the human nature remain indissolubly united even after the Resurrection — that we might know the Word to be not distinct from His flesh — and confess one Son of God to be both Word and flesh.

Eutyches is utterly void of this mystery of the faith, recognizing our nature in the only-begotten Son of God neither in the humility of the mortality He assumed nor in the glory of the resurrection. Nor did he fear the declaration of the blessed apostle and evangelist John: Every spirit that confesses that Jesus Christ has come in the flesh is from God; and every spirit that dissolves Jesus is not from God, and this is the Antichrist (1 John 4:2–3). But what is to “dissolve Jesus” if not to separate the human nature from Him and to void, by shameless fictions, the one mystery through which we have been saved?

Blind to the nature of Christ’s body, Eutyches must err equally about His passion. For if he does not believe the Lord’s cross to be false and genuinely accepts the torment borne for the world’s salvation, let him acknowledge the flesh of Him whose death he credits — and not deny the man of our substance in Him whom he knows was capable of suffering. To deny the truth of the flesh is to deny the reality of the bodily passion. If the Christian faith is genuinely accepted, and the Gospel is not turned away from, let him behold what nature it was that hung pierced upon the cross — and from the soldier’s lance opening the crucified side let him understand whence blood and water flowed, to water the Church with font and cup (John 19:34).

Let him hear the blessed apostle Peter: Redeemed…by the precious blood of Jesus Christ, as of a lamb without blemish or spot (1 Pet. 1:18–19). Let him not skip over what the same apostle says: Christ therefore having suffered in the flesh, be you also armed with the same thought (1 Pet. 4:1). Let him not resist the blessed John: The blood of Jesus, the Son of God, cleanses us from all sin (1 John 1:7), and: This is the victory that overcomes the world, our faith. Who is it that overcomes the world but he who believes that Jesus is the Son of God? This is He who came by water and blood, Jesus Christ; not by water alone, but by water and blood. And the Spirit is the one that bears witness, because the Spirit is truth. For there are three that bear witness: the Spirit, and the water, and the blood; and these three agree (1 John 5:4–8). The Spirit of sanctification, the blood of redemption, and the water of baptism are indivisible — the Catholic Church lives by this faith and grows by it, believing in Christ neither a humanity without true divinity nor a divinity without true humanity.

Chapter VI: Against Those Who Assert Two Natures Before the Union but One After; An Appeal for Eutyches’s Repentance

When Eutyches, at your examination, responded and said: I confess that our Lord was of two natures before the union; but after the union I confess one nature3 — I marvel that so absurd and perverse a profession was not censured by the judges and that so foolish and blasphemous a statement was passed over as if no offense had been given. It is as impious to say that the only-begotten Son of God was of two natures before the Incarnation as to assert one nature after the Word became flesh.

Lest Eutyches think his view right or tolerable simply because it was not rebuked by your sentence, We urge your diligence, dearest brother, that if, through the mercy of God, the matter comes to a satisfactory conclusion, this imprudent man may be cleansed of the poison of his error as well. As the acts show, he began well enough by renouncing his own persuasion, professing what he had not said and accepting what he had previously refused. But when he declined to anathematize his impious dogma, your brotherhood rightly perceived that he remained in his perfidy and merited the judgment of condemnation.

If he now sincerely repents and understands that the episcopal authority acted justly against him, or fully condemns his error by word and by written subscription, no mercy shown to one who has made correction is blameworthy. Our Lord, the true and good shepherd, who laid down His life for His sheep (John 10:11) and came to save souls, not to destroy them (Luke 9:56), desires us to imitate His piety — restraining the erring through justice and not repelling those who return through severity. The truest defense of the faith is made when a false opinion is condemned even by those who previously held it.

For the pious and faithful handling of this entire cause, We have dispatched Our brothers — Our fellow bishop Julius, and the priest Renatus of the title of Saint Clement, and my son the deacon Hilarius — to act in Our stead; and with them Our notary Dulcitius, whose proved faith is known to Us.4 They will supply your brotherhood with Our full instructions on all that must be decreed in this matter. May God keep you safe, dearest brother.

Given on the twelfth day before the Kalends of June, in the consulship of Asturius and Protogenes, most illustrious men.5