Leo, bishop, to the clergy, honorati, and people dwelling at Constantinople.

Chapter I: Joy at Their Fidelity to Flavian; Those Who Deny Christ’s True Humanity Are Confederates of the Manicheans; Leo’s Fatherly Care

Although the memory of what was recently done at the council of priests at Ephesus afflicts Us with much grief — seeing that, as the concurring report has spread and the very outcome of events makes plain, neither the moderation of justice nor the discipline of the faith was maintained there — We nonetheless rejoice in the piety of your devotion, and have confirmed the affection of all of you from the acclamations of the holy people, copies of which have been brought to Us: because the just love of the best father lives and persists in good sons, and you do not permit the learning of Catholic doctrine to be corrupted in any part.1 For beyond doubt, as the Holy Spirit has revealed to you, those who deny that the true man of our nature was assumed by the Only-Begotten Son of God are in confederation with the Manichean error — and would have all the bodily actions of the Lord be mere phantasms of a simulacrum.

That you might give no assent to this impiety, We have already directed exhortatory letters to your charity through Our son Epiphanius and Dionysius, notary of the Roman Church — through which We bestowed the confirmation you sought, so that you might not doubt that We bestow fatherly care upon you, and labor by every means so that, with the mercy of God helping, all the scandals stirred up by the rash and the foolish may be destroyed.2 Nor should anyone dare to flatter himself on sacerdotal honor who could be shown in the execrable impiety of corrupted understanding — for if such ignorance is hardly tolerable in laymen, how much less can it be excused in those who preside, nor does it deserve either indulgence or pardon, especially when those who thus presume to defend the commentaries of perverse opinions stir up scandal.

Chapter II: The Truth of Christ’s Flesh Is Proved from the Mystery of the Eucharist; Leo’s Prayer for the Constantinople Faithful

Let such things be held in contempt by the holy members of the body of Christ, and let not the Catholic freedom suffer the yoke of the faithless to be imposed upon it. Outside the gift of divine grace and outside the mystery of salvation are to be counted those who, denying the nature of our flesh in Christ, contradict the Gospel, and are reluctant to accept the Symbol. Nor do they perceive that their blindness has brought them to this: that they do not hold the truth either of the Lord’s passion or of His resurrection — because both are made void in the Savior if the flesh of our race is not believed in Him. In what darkness of ignorance, in what torpor of laziness have they lain until now, that they have not discerned by hearing, or come to know by reading, what is so consonant in the mouth of all in God’s Church that not even from the lips of infants is the truth of the body and blood of Christ kept silent in the mysteries of communion? For in that mystical distribution of spiritual nourishment this is imparted, this is received: that we, receiving the power of the heavenly food, pass over into the very flesh of Him who became our flesh. And to confirm your charity, which with laudable faith stands firm against the enemies of the truth, fittingly and opportunely I make use of the word and sentiment of the Apostle: Because of this I also, hearing of your faith which is in the Lord Jesus, and of your love toward all the saints, do not cease to give thanks for you, making mention of you in my prayers: that the God of our Lord Jesus Christ, the Father of glory, may give you a spirit of wisdom and revelation in the knowledge of Him, the eyes of your heart enlightened (Eph. 1:15–18) — that He has put all things under His feet, and has given Him as head over all things to the Church, which is His body, the fullness of Him who fills all in all (Eph. 1:22–23).

Chapter III: The Incarnation Proved from the Genealogy of the Human Race; Why the Son Was Sent in the Fullness of Time

Let the adversaries of the truth say here what the Father willed when He willed to advance His Son over all things through the nature derived from Adam — or to what substance He subjected all things. For God in all things, and in those consubstantial with Himself, has placed all things under the Father; and the sempiternal power of the One Who generates and the One Who is generated is co-eternal. The Creator of all natures, since all things were made through Him and without Him was made nothing (John 1:3), is superior to all things He has founded; what belongs to Him properly is to rule over everything He has created, and what is subordinate is to be everything He has established. Neither is anything His own or sempiternal derived apart from the Father, nor does anything He has established derive from anything other than what the Father has made through Him. Therefore the nature He willed to raise above all things is the one that He had subjected to the power of all things: so that neither should He raise what is His own, nor advance as a subject what is alien. This is the human nature, which neither by its own power could lift itself, nor could any alien lordship promote it. It is therefore the body of Christ which, constituted from the flesh of the human race, freed from all sin through the sanctification of the Holy Spirit, took on the form of a servant (Phil. 2:7). The truth of our nature and of our blood was assumed from the Virgin, and was similar to us in all things — except that in Him there was no stain of sin.

Chapter IV: The Necessity of the Incarnation for the Redemption of Adam’s Race

For such was the cause of mortality transmitted from the first parents — that original sin, passing through posterity, left no one exempt from the condemnation of damnation — that, unless the Word became flesh and dwelt among us (John 1:14), namely in that nature which was of our race and lineage, no one could escape the penalty of the ancient fall. Therefore the Apostle says: As by one man’s transgression condemnation came upon all men, so also by one man’s righteousness justification of life comes upon all men. For just as by the disobedience of one man many were constituted sinners, so also by the obedience of one man many shall be constituted just (Rom. 5:18–19). And again: For since by a man came death, also by a man came the resurrection of the dead. For as in Adam all die, so also in Christ shall all be made alive (1 Cor. 15:21–22). All of these, who have been found born of Adam, having the testimony of faith and the grace of justification and communion of nature — whoever denies that this nature was assumed by the Only-Begotten Son of God in the womb of the Davidic Virgin is alien from every mystery of the Christian religion; and not knowing the bride, not knowing the bridegroom, cannot be present at the wedding feast. For the flesh of Christ is the veil of the Word, by which all who confess Him fully are clothed. But whoever recoils from it and counts it unworthy will have no ornament from it — and however boldly such a one inserts himself into the royal feast and presumes to mix at the sacred banquet, he cannot deceive the king’s scrutiny; but, as the Lord himself has declared, he will be bound hand and foot and cast into the outer darkness, where there will be weeping and gnashing of teeth (Matt. 22:13).

Chapter V: Against Various Errors Concerning the Incarnation; Closing Appeal to Persevere and Pray for the Italian Council

Therefore we do not say that Christ is only God, as the Manichean heretics do; nor only man, as the Photinian heretics do; nor so much of a man that anything is lacking that is certain to pertain to human nature — whether soul, or rational mind, or flesh, which He did not take from a woman, as the Apollinarists and Valentinians assert. Nor do we say that the blessed Virgin Mary conceived a man without the Son of God, who was subsequently received by the Word — which is the view of Nestorius, whom we have rightly and justly condemned. But we say that Christ, the Son of God, is true God, born of God the Father without any beginning of time; and is equally true man, born of a mother who is human at the fullness of time: nor does His humanity, of which the Father is greater, diminish anything of His nature that is equal to the Father. And this same is one Christ, who most truly said in accordance with His divinity: I and the Father are one (John 10:30); and in accordance with His humanity: The Father is greater than I (John 14:28). Hold this true and indissoluble faith, dearest ones — which alone makes true Christians, and which, as we understand and are confident, you defend with devoted earnestness and laudable love — hold it perseveringly and assert it constantly.

And since it is fitting that you also, after divine help, merit the favor of Catholic princes — humbly and wisely petition that to Our request, by which We have asked that a full synod be convened, the most clement emperor deign to assent: by which, the sooner, with the mercy of God helping, the strength of the sound may be increased, and medicine may be provided for the sick, if they consent to be healed.3