Leo, bishop, to Leo, Augustus.

Chapter I: Leo Fulfills His Promise of a Fuller Exposition of the Faith, That the Ember of Meditation May Flame Into Light

I recall promising you, venerable emperor, in the matter of the faith about which I know your piety to be devoutly concerned, that a fuller account of my humble thoughts was forthcoming. I now fulfill that promise with the Lord’s help, through this favorable occasion, that instruction useful to your holy zeal may, as far as I am able to judge, not be wanting. Though I know that your clemency has no need of human teaching, and has drawn the purest doctrine from the abundant gift of the Holy Spirit, it is nonetheless part of my duty of office to make clear what you already understand and to proclaim what you already believe1 — so that that fire which the Lord came to cast upon the earth (Luke 12:49), stirred by the frequent motion of meditation, may so glow that it burns, and so burn that it gives light. The Eutychian heresy has striven to cast great darkness over the Eastern regions, and has attempted to turn the eyes of the untaught away from that light which, as the Gospel says, shines in the darkness and the darkness could not overcome it (John 1:5). Having fallen back into its own blindness, it now breaks out afresh in the disciples from what it had lost in its founder.

Chapter II: The Two Heresies of Nestorius and Eutyches Are Set Out and Anathematized

Within a brief span of time the Catholic faith — which is unique and true, to which nothing can be added and nothing taken away — was assailed by two enemies: Nestorius arose first, Eutyches second, and each tried to bring two heresies into the Church of God that appeared to be opposites, so that each deserved to be condemned by the preachers of truth, since what both held in their varied falsehood was equally mad and sacrilegious.

Let Nestorius be anathematized,2 then — who believed the Blessed Virgin Mary to be mother not of God but of a man only, and so made one person of the flesh and another of the Deity; who failed to hold that in the Word of God and in the flesh there was one Christ, but preached separately and distinctly a Son of God on the one side and a man on the other. Yet with the unchangeable essence of the Word — coeternal and co-temporal with the Father and the Holy Spirit — remaining what it was, the Word was so made flesh within the Virgin’s womb that through this ineffable mystery, in one conception and one birth, and according to the truth of each nature, the same virgin was both handmaid and mother of the Lord. This Elizabeth also understood, as the evangelist Luke records, when she said: Why has this happened to me, that the mother of my Lord should come to me? (Luke 1:43).

Let Eutyches also be struck by the same anathema — who, rolling through the impious errors of earlier heretics, selected the third doctrine of Apollinaris: denying the truth of human flesh and soul throughout our Lord Jesus Christ, and asserting that he was of one nature only, as though the Deity of the Word had transformed itself into flesh and soul. According to him, all of Christ — being conceived and born, being nourished and growing, being crucified and dying, being buried and rising again, ascending into heaven, and sitting at the Father’s right hand from where he will come to judge the living and the dead — belonged to the divine essence alone, which receives none of these things without the truth of flesh. For the nature of the Only-begotten is the nature of the Father and of the Holy Spirit — equally impassible, equally unchangeable, the indivisible unity and consubstantial equality of the eternal Trinity. And so if any Eutychian parts from Apollinaris’s perversity in order not to be convicted of holding the Deity passible and mortal, and yet dares to assert one nature of the incarnate Word — that is, of the Word and the flesh — he falls manifestly into the madness of Valentinus and Manes, and believes that the Lord Jesus Christ, mediator of God and humanity, acted out everything in a merely theatrical way, and that it was not a real human body in him but only a phantom of a body that appeared to the eyes of beholders.

Chapter III: The Nicene Creed Confounds All These Monstrous Heresies

Since the Catholic faith has long detested these lying impieties, and the sacrileges of such assertions have long been condemned by the unanimous voices of the blessed Fathers throughout the whole world, there is no doubt that we preach and defend the same faith that the holy Council of Nicaea confirmed, saying:3

We believe in one God the Father Almighty, maker of all things visible and invisible. And in one Lord Jesus Christ, the Son of God, the only-begotten, born of the Father — that is, of the substance of the Father — God from God, light from light, true God from true God, born not made, of one substance with the Father (which the Greeks call homoousios), through whom all things were made, both in heaven and on earth; who for us and for our salvation came down, was incarnate and made man, suffered and rose again on the third day, ascended into the heavens, and shall come to judge the living and the dead. And in the Holy Spirit.

In this profession of faith it is most clearly contained what we also confess and believe about the Lord’s Incarnation — that in order to restore humanity, he brought with him no flesh from heaven, but took true flesh of our frailty within the womb of his Virgin Mother.

Chapter IV: The Reconciliation of Humanity Depends on the Incarnation: Without It Christ Fulfills Neither the Office of Mediator Nor of Redeemer

Let those who are so blinded and so alienated from the light of truth that they deny the truth of human flesh to the Word of God from the moment of the Incarnation — let them show in what sense they claim the name of Christian for themselves, and explain how they are in accord with the truth of the Gospel. For as the evangelist cannot be denied to say, the Word was made flesh and dwelt among us (John 1:14), so it cannot be denied, as the blessed Paul declares, that God was in Christ reconciling the world to himself (2 Cor. 5:19). But what reconciliation could there have been, to restore God’s favor to the human race, unless the mediator of God and humanity had taken upon himself the cause of all? And by what reasoning would he have fulfilled the truth of a mediator, unless the One who in the form of God is equal to the Father had also become, in the form of a servant, a sharer in our condition — so that the bond of death contracted by one man’s transgression might be dissolved by one man’s death? For the outpouring of Christ’s blood for the unjust was so rich a ransom that, if all the captives had believed in their Redeemer, the chains of the devil would have held none of them. As the Apostle says: where sin abounded, grace has much more abounded (Rom. 5:20). And since those born under the condemnation of sin have received the power to be reborn into justice, the gift of freedom has been made more powerful than the debt of servitude.

Chapter V: It Was by Christ’s Sacrifice Alone That the World Was Reconciled to God and Sinners Justified

What hope, then, do those leave themselves who deny the truth of the human body in our Savior, and withdraw themselves from the shelter of this mystery? Let them say by what sacrifice they were reconciled, by what blood they were redeemed. Who is it, as the Apostle says, who gave himself up for us as an offering and sacrifice to God as a fragrant aroma? (Eph. 5:2). Or what sacrifice was ever more sacred than what the true and eternal High Priest4 placed upon the altar of the cross through the immolation of his own flesh? For although the deaths of many holy ones in the sight of the Lord are precious (Ps. 115:15), the slaying of no innocent person was itself the world’s redemption. The just received crowns — they did not give them. The examples born of faithful endurance gave rise to patterns of patience, not gifts of justification. The Lord paid one by one what he owed to each in turn: for among the sons of humanity, our Lord Jesus Christ alone, who was truly the spotless Lamb, was the one in whom all were crucified, all died, all were buried, and all too were raised. Of them he himself said: When I am lifted up from the earth, I will draw all things to myself (John 12:32). True faith, then — justifying the ungodly and creating the just — drawn to take part in his humanity, finds salvation in him alone, in whom a human being alone finds himself innocent: free to glory through the grace of God in his power, who in the humility of our flesh made war against the enemy of the human race and gave his victory to those in whose body he triumphed.

Chapter VI: The Properties of Each Nature in Christ Are Manifested Through His Different Actions

Although in the one Lord Jesus Christ, true Son of God and true Son of Man, the person of the Word and the flesh is one — inseparably and indivisibly sharing all common actions — the qualities of each set of those actions must nonetheless be discerned. Those who contemplate with sincere faith must perceive what humility of the flesh brings about and what the height of the Deity inclines toward: what it is that the flesh does not do without the Word, and what it is that the Word does not accomplish without the flesh. Without the power of the Word, the Virgin would neither have conceived nor given birth; and without the truth of flesh, the Infant wrapped in cloths would not have lain in a manger. Without the power of the Word, the Magi would not have adored the child announced by the star; and without the truth of flesh, the child would not have been taken to Egypt and hidden from Herod’s persecution. Without the power of the Word, the Father’s voice sent from heaven would not have said: This is my beloved Son in whom I am well pleased (Matt. 3:17); and without the truth of flesh, John would not have proclaimed: Behold the Lamb of God, behold him who takes away the sin of the world (John 1:29). Without the power of the Word, the healing of the crippled and the raising of the dead would not have taken place; and without the truth of flesh, neither food would have been needed by the hungry nor sleep by the weary. Finally, without the power of the Word, the Lord would not have declared himself equal to the Father; and without the truth of flesh, he would not have said that the Father is greater than himself (John 14:28). For the Catholic faith embraces both and defends both, confessing the one Lord Jesus Christ as the living Son of God and as both Word and man. So although from that beginning — when the Word was made flesh in the Virgin’s womb — no division between the forms ever existed, and all the actions of the whole person throughout every stage of his bodily growth were those of one person, we do not confuse what was done inseparably, but discern by the quality of the actions to which form each belongs.

Chapter VII: The Truth of Christ’s Flesh Is Proved From the Truth of His Death, Burial, and Resurrection

Let those hypocrites then — who refuse to receive the light of truth in their blind minds — explain: in which form was the Lord of majesty nailed to the wood of the cross; what lay in the tomb; and when the stone was rolled away, what flesh rose on the third day — and in what form, after the resurrection, did he rebuke certain disciples who still did not believe, and refute the hesitation of doubters, when he said: Touch me and see, for a spirit does not have flesh and bones, as you see me having (Luke 24:39)? And to the apostle Thomas: Put your hand into my side, and see my hands and my feet, and do not be faithless but believing (John 20:27)? By this very manifestation of his body he was already destroying the lies of heretics, so that the whole Church, formed in Christ’s teaching, would not doubt what it must believe — the very thing the apostles had received to preach. Yet if even in so great a light of truth heretical obstinacy will not lay down its own darkness, let them show where they derive for themselves the hope of eternal life, to which no one can come except through the mediator of God and humanity, the man Christ Jesus. As the blessed apostle Peter says: There is no other name given under heaven among men by which we must be saved (Acts 4:12); nor is there any redemption of human captivity except in his blood — of him who gave himself as a ransom for all (1 Tim. 2:6), and who, as the blessed apostle Paul proclaims, though he was in the form of God did not count equality with God a thing to be grasped, but emptied himself, taking the form of a servant, made in the likeness of men, and found in appearance as a man —

Chapter VIII: Christ’s Exaltation Could Not Have Been Accomplished Except in His True Human Nature

— he humbled himself, becoming obedient unto death, even death on a cross. Therefore God also exalted him and gave him the name that is above every name: that at the name of Jesus every knee should bow, in heaven and on earth and under the earth, and every tongue confess that the Lord Jesus Christ is in the glory of God the Father (Phil. 2:6–11).

Since, then, the Lord Jesus Christ is one, and the very same person of verest Deity and verest humanity truly one in him, we understand that the exaltation by which God exalted him and gave him the name that excels all — as the teacher of the nations says — pertains to that form which needed the enrichment of so great a glorification. In the form of God the Son was equal to the Father, and between the Begetter and the Only-begotten there was no distinction in essence, no diversity in majesty; nor had anything been taken from the Word through the mystery of the Incarnation that would need to be restored to him as the Father’s gift. The form of a servant, through which the impassible Deity fulfilled the mystery of great piety, is the human humility that was raised to the glory of divine power — united from the very moment of the Virgin’s conception in such close oneness of Deity and humanity that neither the divine things were transacted without the man, nor the human without God. For this reason, just as the Lord of majesty is said to have been crucified, the One who in his eternity is equal to God is also said to have been exalted: because with the unity of the person remaining inseparable, one and the same is wholly the Son of Man by reason of the flesh, and wholly the Son of God by reason of his one Deity with the Father. Whatever, therefore, Christ received in time, he received as man — so that what he had not possessed as man might be conferred upon him. For according to his Deity the Son possesses without distinction everything the Father possesses; and what in the form of a servant he received from the Father, the same he gave in the form of God. For according to the form of God, the Father and the Son are one (John 10:30); but according to the form of a servant, he came not to do his own will but the will of him who sent him (John 5:30). According to the form of God, as the Father has life in himself, so also he gave the Son to have life in himself (John 5:26); but according to the form of a servant, his soul was troubled even unto death (Matt. 26:38). And the same One is, as the Apostle proclaims, both rich and poor. Rich — because, as the evangelist says, In the beginning was the Word, and the Word was with God, and the Word was God; this, that is the Word, was in the beginning with God (John 1:1–3). Poor — because for our sake the Word was made flesh and dwelt among us (John 1:14). Now the original bonds of our captivity could not be dissolved unless there existed a man whom the prejudice of sin did not hold, who would dissolve with his own spotless blood that lethal contract — as was divinely foreordained from the beginning, and so brought to pass in the fullness of the appointed time: that the promise foretold in so many ways might come to its long-awaited fulfillment, and there might be no doubt about what had been announced through unbroken testimonies throughout all the ages. The manifest wickedness of the heretics is therefore treading on sacred ground when, under the pretext of honoring the Deity, they deny the truth of the human body in Christ, piously supposing that it should be believed that in our Savior nothing is real which saves — even though the whole world, according to the promise that runs through all the ages, has been reconciled with God in Christ; for unless the Word had deigned to become flesh, no flesh could ever have been saved. The entire mystery of the Christian faith is robbed of its radiance — as the heretics would have it — if the light of truth is thought to have lain hidden under the deception of a phantom. Therefore let no Christian be ashamed of the truth of Christ’s body: for all the apostles and their disciples, and all the illustrious doctors of all the Churches, who arrived at the crown either of martyrdom or of confession, shone in the light of this faith, sounding everywhere in unison that in the Lord Jesus Christ one person of Deity and flesh must be confessed.

Chapter IX: Those Who Deny the Truth of Christ’s Body Dishonor the Deity and Lose All Hope of Salvation

For what human reasoning supports those who deny the truth of Christ’s body, when law did not cease to testify to it, prophecy did not cease to foretell it, the Gospels did not cease to teach it, and Christ himself did not cease to show it? Let them search through the whole series of the Scriptures — seeking where the darkness may flee, not how to darken the true light — and through all the ages they will find the truth shining out, so that they may see this great and wonderful mystery believed from the beginning and completed at the end. Since no part of the sacred writings is silent about it, it is enough to have set out certain harmonious signs of truth, so that devotion to the faith may be directed into its fullest breadth, and a sincere intelligence may perceive by its light that in the Son of God — who ceaselessly professes himself the Son of Man and a human being — there is nothing for Christians to be ashamed of, but in which to glory with complete steadfastness.

Chapter X: The Catholic Faith Is Confirmed by the Holy Fathers’ Tradition; the Emperor Is Above All Worthy to Be Its Protector

But so that your piety may recognize that our preaching is at one with the proclamations of the venerable Fathers, I have thought it right to append certain of their statements to this letter. If you will examine them, you will find that we preach nothing other than what the holy Fathers throughout the whole world have taught — and that we differ from no one among them except only the impious heretics.5 With these things briefly set forth, most glorious and venerable emperor, you will recognize with a faith divinely inspired in you that our preaching is united with that of the Fathers, and that in nothing do we differ from the evangelical and apostolic teaching, or from the symbol of Catholic profession. For as the blessed apostle Paul teaches: Great is the mystery of godliness, which was manifested in the flesh, justified in the Spirit, appeared to the angels, was preached among the Gentiles, was believed in the world, was taken up in glory (1 Tim. 3:16). What then is more useful for your salvation? What more fitting to your power? Than that you look to the peace of the Lord’s Churches with the greatest care, and defend the gifts of God in all who are subject to you, suffering no servant of the devil to afflict anyone to their destruction through his malice — so that you who in this present age hold eminence in temporal dominion may merit to reign forever with Christ.

Given on the sixteenth day before the Kalends of September, in the consulship of Leo and Majorian, most august Emperors.6