Nestorius

"Now do we say that the nature of the Word became flesh by undergoing change, nor that it was transformed into an entire man of soul and body; rather do we say that the Word, in a manner indescribable and incomprehensible, personally (hypostatically) united to Himself flesh animated by a rational soul, and thus became Man and was called the Son of Man..."

"Anathema 1. If anyone does not confess that the Emmanuel is in truth God, and that the Holy Virgin is, in consequence, Theotokos (Mother of God), since she brought forth according to the flesh the Word of God who has become flesh, let him be anathema."

"Fragments of the schisms came to mind, passages from the heresies that had divided the Western and Eastern Churches for centuries. Here Nestorius contested the title of Mother of God given to the Virgin, since, in the mystery of the Incarnation, she had carried a human creature in her womb and not God."

"Nestorius, a follower of the Antiochian school where he had been trained, argued that in order to preserve the integrity of Christ's humanity, the divine person of the Word cohabited with the person of the man Jesus, with the consequence that in Christ, according to him, there are two natures and two persons, and Mary can only be called the mother of Christ and not the mother of God."

"Nestorius reaffirms the unity of Christ despite the distinction between the natures, opposing the doctrine of Cyril of the single nature; he speaks of the “person” of the Son, in whom the relationship between the two natures is realised in a manner that is completely different from any other possible relationship between God and human beings. Nestorius is therefore careful to avoid the accusation of Christological dualism."

"Now, first of all, they believed in an orthodox manner in the preaching of the Apostles who lived [at the time of] Constantine [...]. Later, Satan, who has been the enemy of man since ancient times, rose up and seduced the people of the land of Byzantium, and they corrupted the Faith of Christ and introduced heresy into the Church of God through the mouth of Nestorius."

"The error of Nestorius, who refused to acknowledge that Blessed Mary is the Mother of God, is likewise excluded. Both Creeds assert that the Son of God was born or was made flesh of the Virgin Mary. The woman of whom any person is born is called his mother, for the reason that she supplies the matter for human conception. Hence the Blessed Virgin Mary, who provided the matter for the conception of the Son of God, should be called the true mother of the Son of God. As far as the essence of motherhood is concerned, the energy whereby the matter furnished by a woman is formed, does not enter into the question. She who supplied matter to be formed by the Holy Spirit is no less a mother than a woman who supplies matter that is to be formed by the energy latent in male seed. If anyone insists on maintaining that the Blessed Virgin ought not to be called the Mother of God because flesh alone and not divinity was derived from her, as Nestorius contended, he clearly is not aware of what he is saying. A woman is not called a mother for the reason that everything that is in her child is derived from her. Man is made up of body and soul; and a man is what he is in virtue of his soul rather than in virtue of his body. But no man’s soul is derived from his mother. The soul is either created by God directly, as the true doctrine has it, or, if it were produced by transplanting, as some have fancied, it would be derived from the father rather than from the mother. For in the generation of other animals, according to the teaching of philosophers, the male gives the soul, the female gives the body."