On the Incarnation of the Lord (Against Nestorius)

He shows further that this teaching is destructive of the confession of the Trinity.

But still even if your obstinacy and dishonesty are not restrained by this faith of the Creed, are you not, I ask you, overwhelmed by an appeal to reason and the light of truth? Tell me, I ask, whoever you are, O you heretic— At least there is a Trinity, in which we believe, and which we confess: Father and Son and Holy Ghost. Of the Glory of the Father and the Spirit there is no question. You are slandering the Son, because you say that it was not the same Person who was born of Mary, as He who was begotten of God the Father. Tell me then: if you do not deny that the only Son of God was begotten of God, whom do you make out that He is who was born of Mary? You say “a mere man,” according to that which He Himself said: “That which is born of the flesh, is flesh.” But He cannot be called a mere man who was begotten not after the law of human creation alone. “For that which is conceived in her,” said the angel, “is of the Holy Ghost.” And this even you dare not deny, though you deny almost all the mysteries of salvation. Since then He was born of the Holy Ghost, and cannot be termed a mere man, as He was conceived by the inspiration of God, if it is not He who, as the Apostle says, “emptied Himself by taking the form of a servant,” and “the word was made flesh,” and “humbled Himself by becoming obedient unto death,” and “who for our sakes, though He was rich, became poor,” tell me, then, who He is, who was born of the Holy Ghost, and was conceived by the overshadowing of God? You say that He is certainly a different Person. Then there are two Persons; viz., the one, who was begotten of God the Father in heaven; and the other who was conceived of Mary, by the inspiration of God. And thus there is a fourth Person whom you introduce, and whom (though in words you term Him a mere man) you assert actually not to have been a mere man, since you allow (not however as you ought) that He is to be honoured, worshipped, and adored. Since then the Son of God who was begotten of the Father is certainly to be worshipped, and He who was conceived of Mary by the Holy Ghost is to be worshipped, you make two Persons to be honoured and venerated, whom you so far sever from each other, as to venerate each with an honour special and peculiar to Him. And thus you see that by denying and by severing from Himself the Son of God, you destroy, as far as you can, the whole mystery of the divinity. For while you are endeavouring to introduce a fourth Person into the Trinity, you see that you have utterly denied the whole Trinity.