Romans 9:1

And again, if the impious say, How will there not be three Gods and three Persons, on the supposition that they have one and the same divinity? we shall reply: Just because God is the Cause and Father of the Son; and this Son is the image and offspring of the Father, and not His brother; and the Spirit in like manner is the Spirit of God, as it is written, “God is a Spirit.” And in earlier times we have this declaration from the prophet David: “By the word of the Lord were the heavens stablished, and all the power of them by the breath (spirit) of His mouth.” And in the beginning of the book of the creation it is written thus: “And the Spirit of God moved upon the face of the waters.” And Paul in his Epistle to the Romans says: “But ye are not in the flesh, but in the Spirit, if so be that the Spirit of God dwell in you.” And again he says: “But if the Spirit of Him that raised up Jesus …

34. I think that you cannot fail to understand this too, that the word “father” is but a single term indeed, and yet one admitting of being understood in various ways. For one is called father, as being the parent of those children whom he has begotten in a natural way; another is called father, as being the guardian of children whom he has but brought up; and some, again, are called fathers in respect of the privileged standing accruing through time or age. Hence our Lord Jesus Christ Himself is said to have a variety of fathers: for David was called His father, and Joseph was reckoned to be His father, while neither of these two was His father in respect of the actuality of nature. …

28. It is also written, “But I say unto you, Swear not at all.” But the Apostle himself has used oaths in his Epistles. And so he shows how that is to be taken which is said, “I say unto you, Swear not at all:” that is, lest by swearing one come to a facility in swearing, from facility to a custom, and so from a custom there be a downfall into perjury. And therefore he is not found to have sworn except in writing, where there is more wary forethought, and no precipitate tongue withal. And this indeed came of evil, as it is said, “Whatever is more than these is of evil:” not however from evil of his own, but from the evil of infirmity which was in them, in whom he even in this way endeavored to work faith. For that he used an oath in speaking, while not writing, I know not that any Scripture has related concerning him. …

3. "I speak the truth in Christ," says the apostle, "I lie not, my conscience bearing me witness in the Holy Ghost, that I have great heaviness and continual sorrow of heart. For I could wish that myself were accursed from Christ, for my brethren, my kinsmen according to the flesh: who are Israelites; to whom pertaineth the adoption, and the glory, and the covenants, and the giving of the law, and the service and the promises; whose are the fathers, and of whom, as concerning the flesh, Christ came, who is over all, God blessed for ever." Here is the most abundant and express testimony and the most solemn commendation. …

Rom. IX. 1 “I say the truth in Christ, I lie not, my conscience also bearing me witness in the Holy Ghost.” Did I not seem yesterday to you to have spoken some great and exorbitant things of Paul’s love toward Christ? And great indeed they were, too great for any words to express. Yet what you have heard to-day are as far above those things, as those things were above ours. And yet I did not think they could be exceeded, still when I came to what has been read to-day it did appear far more glorious than the whole of the former. And that he was aware of this himself he shows by his exordium. …

I have already in another letter informed your holiness how openly the calumniators of our teaching are slandering us. Now in like manner by means of the very godly bishops I do the same, having not only these as witnesses of the orthodoxy of my teaching but also countless other men who are my hearers in the churches of the East. Above and beyond all these I have my conscience, and Him who sees my conscience. And I know too how the divine Apostle often appealed to the testimony of his conscience, for “our rejoicing is this, the testimony of our conscience” and again “I say the truth in Christ I lie not, my conscience also bearing me witness in the Holy Ghost.” Know then, O holy and godly sir, that no one has ever at any time heard us preaching two sons; in fact this doctrine seems to me abominable and impious, for there is one Lord Jesus Christ through whom are all things. …