To the most religious and God-beloved Bishop Nestorius, Cyril sends greeting in the Lord.

I am informed that there are some who are rashly talking of the character of the faith of the holy Fathers, and are daring to set themselves against it, as if they were not followers of it; and among these, I hear, your Holiness's writings also are circulating, and that they are said to be not quite untainted by error. And indeed, a book was put into my hands, containing many of your little works, and I read it all. And though I was grieved, and greatly distressed, to see that you had strayed from the right path, and were making shipwreck of the faith; yet, that I might not seem to be acting with undue haste, I refrained from writing to you, until I had satisfied myself, either by your own words, or by the testimony of others, that what I heard was true. But since I am now fully persuaded that you are indeed the author of these writings, I have thought it necessary to address you, and to lay before you, not only the faith of the holy Fathers, but also my own, which is in all things agreeable to theirs; hoping that, when you have heard it, you will abandon your errors, and return to the right way.

Now, the holy and great Synod of Nicæa, by the inspiration of God, has set forth to us the faith, which is believed throughout the whole world, and which is in all things agreeable to the holy Scriptures. And this faith, the holy Fathers who assembled at Nicæa, being taught by the Holy Ghost, have delivered to us, that we may believe in one God, the Father Almighty, Maker of all things visible and invisible: And in one Lord Jesus Christ, the Son of God, begotten of the Father, only-begotten, that is, of the substance of the Father, God of God, Light of Light, very God of very God, begotten, not made, being of one substance with the Father, by whom all things were made, both in heaven and on earth: Who for us men, and for our salvation, came down from heaven, and was incarnate by the Holy Ghost of the Virgin Mary, and was made man, and suffered, and rose again the third day, and ascended into heaven, and shall come again to judge the quick and the dead. And in the Holy Ghost. But those who say, There was a time when He was not; and, He was not before He was made; and, He was made of nothing, or of another hypostasis or substance; or, The Son of God is mutable or alterable; these the Catholic and Apostolic Church anathematizes.

This faith, which was set forth by the holy Synod of Nicæa, is the faith of all the holy Churches of God throughout the whole world; and it is the faith which we confess, and which we preach, and by which we are saved. But since your Holiness, as I hear, has introduced new and strange doctrines, which are contrary to this faith, and which are calculated to disturb the minds of the simple, and to corrupt the purity of the faith; I have thought it necessary to warn you, and to exhort you, in the Lord, to cease from these innovations, and to return to the ancient faith of the Church.

For it is written, 'Stand ye in the ways, and see, and ask for the old paths, where is the good way, and walk therein, and ye shall find rest for your souls.' (Jer. vi. 16.) And again, 'Remove not the ancient landmark, which thy fathers have set.' (Prov. xxii. 28.) And again, 'If any man preach any other gospel unto you than that ye have received, let him be accursed.' (Gal. i. 9.)

Now, the holy Fathers, following the example of the holy Scriptures, have always confessed that the only-begotten Son of God, who is of the substance of the Father, and is God of God, Light of Light, very God of very God, by whom all things were made, both in heaven and on earth, for us men, and for our salvation, came down from heaven, and was incarnate by the Holy Ghost of the Virgin Mary, and was made man. And they have always confessed that the Virgin Mary is the Mother of God; not as if the nature of the Word had begun to exist from her, but because from her was born that holy body, animated by a rational soul, to which the Word was substantially united, and therefore He is said to have been born according to the flesh.

For we do not say that the nature of the Word was changed into the nature of the flesh, or that it was transformed into a whole man, consisting of soul and body; for the Word is immutable and unchangeable, and remains always the same, as it is written, 'Jesus Christ the same yesterday, and to-day, and for ever.' (Heb. xiii. 8.) But we say that the Word, uniting to Himself hypostatically a body animated by a rational soul, suffered in His own flesh, and rose again in His own flesh, and ascended into heaven in His own flesh, and shall come again in His own flesh to judge the quick and the dead.

For if we say that the Word suffered by Himself, or that He was transformed into the nature of the flesh, we shall fall into the error of those who say that the Word is mutable or alterable. But if we say that the Word, uniting to Himself hypostatically a body animated by a rational soul, suffered in His own flesh, and rose again in His own flesh, and ascended into heaven in His own flesh, and shall come again in His own flesh to judge the quick and the dead, we shall confess the true faith, and shall be in agreement with the holy Scriptures, and with the holy Fathers.

For it is written, 'Forasmuch then as the children are partakers of flesh and blood, He also Himself likewise took part of the same; that through death He might destroy him that had the power of death, that is, the devil.' (Heb. ii. 14.) And again, 'Who, being in the form of God, thought it not robbery to be equal with God: but made Himself of no reputation, and took upon Him the form of a servant, and was made in the likeness of men: and being found in fashion as a man, He humbled Himself, and became obedient unto death, even the death of the cross.' (Phil. ii. 6-8.)

And again, 'Christ also hath once suffered for sins, the just for the unjust, that He might bring us to God, being put to death in the flesh, but quickened by the Spirit.' (1 Pet. iii. 18.) And again, 'For in that He Himself hath suffered being tempted, He is able to succour them that are tempted.' (Heb. ii. 18.)

From these passages, and from many others which might be adduced, it is clear that the Word, uniting to Himself hypostatically a body animated by a rational soul, suffered in His own flesh, and rose again in His own flesh, and ascended into heaven in His own flesh, and shall come again in His own flesh to judge the quick and the dead.

Therefore, we confess that the Virgin Mary is the Mother of God, because from her was born that holy body, animated by a rational soul, to which the Word was substantially united, and therefore He is said to have been born according to the flesh. And we anathematize those who say that the Word was not united hypostatically to a body animated by a rational soul, but that He merely dwelt in it, as in a temple; for this is to make two Sons, one the Word, and the other the man, and not one Son, Jesus Christ, the only-begotten Son of God.

For if we say that the Word merely dwelt in the man, as in a temple, we shall fall into the error of those who say that the Son of God is mutable or alterable. But if we say that the Word was united hypostatically to a body animated by a rational soul, we shall confess the true faith, and shall be in agreement with the holy Scriptures, and with the holy Fathers.

And we confess that the Word, uniting to Himself hypostatically a body animated by a rational soul, is one Christ, one Son, one Lord. And we anathematize those who say that there are two Sons, or two Christs, or two Lords; for this is to divide the indivisible, and to separate the inseparable, and to make two Sons instead of one.

For it is written, 'There is one Lord Jesus Christ, by whom are all things, and we by Him.' (1 Cor. viii. 6.) And again, 'One Lord, one faith, one baptism, one God and Father of all, who is above all, and through all, and in you all.' (Eph. iv. 5-6.)

From these passages, and from many others which might be adduced, it is clear that the Word, uniting to Himself hypostatically a body animated by a rational soul, is one Christ, one Son, one Lord.

Therefore, we confess that the Virgin Mary is the Mother of God, because from her was born that holy body, animated by a rational soul, to which the Word was substantially united, and therefore He is said to have been born according to the flesh. And we anathematize those who say that the Word was not united hypostatically to a body animated by a rational soul, but that He merely dwelt in it, as in a temple; for this is to make two Sons, one the Word, and the other the man, and not one Son, Jesus Christ, the only-begotten Son of God.

For if we say that the Word merely dwelt in the man, as in a temple, we shall fall into the error of those who say that the Son of God is mutable or alterable. But if we say that the Word was united hypostatically to a body animated by a rational soul, we shall confess the true faith, and shall be in agreement with the holy Scriptures, and with the holy Fathers.

And we confess that the Word, uniting to Himself hypostatically a body animated by a rational soul, is one Christ, one Son, one Lord. And we anathematize those who say that there are two Sons, or two Christs, or two Lords; for this is to divide the indivisible, and to separate the inseparable, and to make two Sons instead of one.

For it is written, 'There is one Lord Jesus Christ, by whom are all things, and we by Him.' (1 Cor. viii. 6.) And again, 'One Lord, one faith, one baptism, one God and Father of all, who is above all, and through all, and in you all.' (Eph. iv. 5-6.)

From these passages, and from many others which might be adduced, it is clear that the Word, uniting to Himself hypostatically a body animated by a rational soul, is one Christ, one Son, one Lord.

Therefore, let your Holiness, following the example of the holy Fathers, preach and teach the true faith, and cease from these innovations, which are contrary to the faith, and which are calculated to disturb the minds of the simple, and to corrupt the purity of the faith. And if you do this, you will give joy to all the holy Churches of God throughout the whole world, and you will be glorified by God, and by all the holy Fathers.

But if you persist in your errors, and continue to disturb the minds of the simple, and to corrupt the purity of the faith, then I shall be compelled to act against you, according to the canons of the holy Church, and to separate you from the communion of the holy Churches of God throughout the whole world. For it is written, 'If any man preach any other gospel unto you than that ye have received, let him be accursed.' (Gal. i. 9.)

And I pray God that He will give you grace to understand the truth, and to walk in the way of righteousness, and to keep the faith pure and undefiled, to the glory of His holy name, and to the salvation of your soul, and of the souls of those who hear you. Amen.

Dear brothers and sisters,

In our catecheses, we are reflecting on the great figures of the Church of the first centuries. Today, we meet St Cyril of Alexandria, one of the most important Fathers of the Church, particularly renowned for his Christological doctrine. He was the nephew of Theophilus, Patriarch of Alexandria, and was born in about 370 A.D. He received a good education, and he was able to complete his studies in the famous Catechetical School of Alexandria, becoming a monk for some years. In 412, when his uncle Theophilus died, he was elected Patriarch of the important See of Alexandria, which was a true metropolis of the Byzantine Empire, both in power and prestige: it was the second city of the Empire after Constantinople. In addition to the ancient and flourishing Catechetical School, Alexandria also boasted a powerful scientific and cultural institution, the Library and the Museum. Cyril was Patriarch in a city where the ancient Hellenistic paganism was still very influential, even if Christianity had already made great progress. The situation of Christians was not easy: there was considerable tension between them and the different groups of pagans and Jews. This tension was exacerbated by the fact that Alexandria was a city of many factions and parties, and rivalry among them was often very strong, even violent. Cyril, as Patriarch, was a strong and energetic leader, who did not hesitate to exercise his power, in a sometimes authoritarian way, to defend the integrity of the Christian faith and to promote the unity of the Church within his jurisdiction.

In the early years of his episcopacy, Cyril had to face the difficult situation in the city, characterized by strong internal tensions. In 415, he expelled the Jews from Alexandria, and he also had conflicts with the Prefect Orestes. The relationship between the See of Alexandria and the Imperial Court in Constantinople was also strained, especially because of the growing influence of the latter. However, Cyril’s greatest challenge, and the one for which he is most remembered, was the Christological controversy that arose with Nestorius, who became Patriarch of Constantinople in 428. Nestorius taught that in Christ there were two distinct persons, one divine and one human, united by a moral bond. Consequently, he refused to call Mary 'Theotokos', Mother of God, arguing that she was only 'Christotokos', Mother of Christ, because she had given birth only to the human nature of Christ. For Cyril, this teaching was a grave error that contradicted the faith of the Church and undermined the very mystery of the Incarnation. He saw in Nestorius's doctrine a dangerous division of Christ into two separate subjects, which would deny the unity of the divine and human natures in the one person of the Word Incarnate.

Cyril reacted with great determination and theological precision. He immediately wrote to Nestorius, exhorting him to abandon his erroneous views and to return to the orthodox faith. He also wrote to the Emperor Theodosius II and to the Empress Pulcheria, as well as to Pope Celestine I, informing them of Nestorius's errors and seeking their support. Pope Celestine I, after examining the matter, sided with Cyril and condemned Nestorius's doctrine. He authorized Cyril to act as his representative at a Synod to be held in Ephesus, with the task of warning Nestorius and, if he persisted in his errors, of deposing him. Thus, the famous Council of Ephesus, the third Ecumenical Council, was convoked in 431. Cyril presided over the Council, acting as the Pope's legate. Despite many difficulties and delays, due to Nestorius's refusal to attend and the late arrival of some bishops, Cyril decided to open the Council. The Council, after careful examination of Nestorius's writings and Cyril's own theological letters, which were acclaimed as being in conformity with the Nicene Creed, solemnly condemned Nestorius's doctrine and affirmed the unity of Christ's person and the title of Theotokos for Mary. The Council declared that Jesus Christ is one person, the divine Word, who from the moment of the Incarnation assumed human nature, without confusion, change, division, or separation. Therefore, Mary is truly the Mother of God, because she gave birth to the one who is God.

The condemnation of Nestorius and the affirmation of the Theotokos were a great triumph for orthodoxy, but they also led to a period of intense controversy and division. Many Eastern bishops, especially those from Antioch, initially opposed Cyril, accusing him of Apollinarianism (a heresy that denied Christ a human soul). However, through patient dialogue and theological clarification, especially through the 'Formula of Reunion' in 433, a reconciliation was achieved between Cyril and the Antiochene bishops. This formula, while affirming the unity of Christ's person, also explicitly acknowledged the two natures of Christ. Cyril continued to defend the orthodox faith until his death in 444. His theological legacy is immense. He is considered one of the most important Christological theologians of the early Church. His writings, particularly his commentaries on the Gospels, his letters, and his polemical works against Nestorius, are a treasure of profound theological insight. He developed a precise Christology, emphasizing the unity of the person of the Word Incarnate. He taught that the two natures, divine and human, are united in Christ 'without confusion, without change, without division, without separation,' a formula that would later be adopted by the Council of Chalcedon in 451.

Cyril’s insistence on the unity of Christ’s person and the reality of the Incarnation was crucial for the development of Christian doctrine. He understood that if Christ were not truly one divine person, then our salvation would be jeopardized. If Mary were not the Mother of God, then the one she bore would not be God, and thus could not save us. His defense of the Theotokos was not merely about a title for Mary, but about the very identity of Christ and the truth of our redemption. He saw that the denial of the Theotokos was a subtle, yet profound, attack on the reality of the Incarnation, making Christ a mere man inhabited by God, rather than God Himself made man. Cyril’s intellectual rigor and pastoral zeal ensured that the Church maintained the integrity of its faith in the face of grave error. He is rightly venerated as a Doctor of the Church, whose teachings continue to enlighten and guide us in understanding the central mystery of our faith: the Son of God, who for us men and for our salvation, became truly man, born of the Virgin Mary, the Mother of God.