St. Irenaeus [Adversus Haereses, Book III, Chapter 19:1 (circa AD 180)]

The Word says, mentioning His own gift of grace: "I said, You are all sons of the Highest, and gods; but you shall die like men." He speaks undoubtedly these words to those who have not received the gift of adoption, but who despise the incarnation of the pure generation of the Word of God, defraud human nature of promotion into God, and prove themselves ungrateful to the Word of God, who became flesh for them. For it was for this end that the Word of God was made man, and He who was the Son of God became the Son of man, that man, having been taken into the Word, and receiving the adoption, might become the son of God. For by no other means could we have attained to incorruptibility and immortality, unless we had been united to incorruptibility and immortality. But how could we be joined to incorruptibility and immortality, unless, first, incorruptibility and immortality had become that which we also are, so that the corruptible might be swallowed up by incorruptibility, and the mortal by immortality, that we might receive the adoption of sons.

St. Gregory of Nyssa [The Great Catechism, Chapter XXXVII (AD 385)]

Rightly, then, do we believe that now also the bread which is consecrated by the Word of God is changed into the Body of God the Word. For that Body was once, by implication, bread, but has been consecrated by the inhabitation of the Word that tabernacled in the flesh. Therefore, from the same cause as that by which the bread that was transformed in that Body was changed to a Divine potency, a similar result takes place now. For as in that case, too, the grace of the Word used to make holy the Body, the substance of which came of the bread, and in a manner was itself bread, so also in this case the bread, as says the Apostle, "is sanctified by the Word of God and prayer"; not that it advances by the process of eating to the stage of passing into the body of the Word, but it is at once changed into the body by means of the Word, as the Word itself said, "This is My Body." Seeing, too, that all flesh is nourished by what is moist (for without this combination our earthly part would not continue to live), just as we support by food which is firm and solid the solid part of our body, in like manner we supplement the moist part from the kindred element; and this, when within us, by its faculty of being transmitted, is changed to blood, and especially if through the wine it receives the faculty of being transmuted into heat. Since, then, that God-containing flesh partook for its substance and support of this particular nourishment also, and since the God who was manifested infused Himself into perishable humanity for this purpose, viz. that by this communion with Deity mankind might at the same time be deified, for this end it is that, by dispensation of His grace, He disseminates Himself in every believer through that flesh, whose substance comes from bread and wine, blending Himself with the bodies of believers, to secure that, by this union with the immortal, man, too, may be a sharer in incorruption. He gives these gifts by virtue of the benediction through which He transelements the natural quality of these visible things to that immortal thing.

St. Hilary of Poitiers [Homily on Psalm 91]

We are reconciled in the body of His flesh. Therefore by union with the flesh that He assumed, we are in Christ. This is God's mystery, hidden in God for ages and generations and now revealed to His saints, that in Christ we are coheirs, concorporate and comparticipants in the promise of God (Eph. 3:5 6). By union with His flesh, all enter into Christ. He will transform their baseness into the glory of His flesh, on condition that they resist their passions, purify themselves of their stains in the sacrament of the new birth, and remember that henceforth they bear not their own flesh, but Christ's.

St. Augustine [Sermon 71:4-5]

And how do they become the sons of God? "Who were born, not of blood, nor of the will of man, nor of the will of the flesh, but of God." Having received power to become the sons of God, they are born of God. Mark then: They are born of God, "not of blood," like their first birth, like that wretched birth, issuing out of wretchedness. But they who are born of God, what were they? whereby were they first born? Of blood; of the joint blood of the male and female, of the carnal union of male and female, from this were they born. From whence now? They are born of God. The first birth of the male and female; the second birth of God and the Church.

Lo, they are born of God; whereby is it brought to pass that they should be born of God, who were first born of men? Whereby is it brought to pass, whereby? "And the Word was made Flesh, that It might dwell among us." Wondrous exchange; He made Flesh, they spirit. What is this? What condescension is here, my brethren! Lift up your minds to the hope and comprehension of better things. Give not yourselves up to worldly desires. "Ye have been bought with a Price; " for your sakes the Word was made Flesh; for your sakes He who was the Son of God, was made the Son of man: that ye who were the sons of men, might be made sons of God. What was He, what was He made? What were ye, what were ye made? He was the Son of God. What was He made? The Son of man. Ye were the sons of men. What were ye made? The sons of God. He shared with us our evil things, to give us His good things. But even in that He was made the Son of man, He is different much from us. We are the sons of men by the lust of the flesh; He the Son of man by the faith of a virgin. The mother of any other man whatever conceives by a carnal union; and every one is born of human parents, his father and his mother. But Christ was born of the Holy Ghost, and the Virgin Mary. He came to us, but from Himself departed not far; yea from Himself as God He departed never; but added what He was to our nature. For He came to that which He was not, He did not lose what He was. He was made the Son of man; but did not cease to be the Son of God. Hereby the Mediator, in the middle. What is, "in the middle"? Neither up above, nor down below. How neither up above, nor down below? Not above, since He is Flesh; not below, since He is not a sinner. But yet in so far as He is God, above always. For He did not so come to us, as to leave the Father. From us He went, and did not leave us; to us will He come again, and will not leave Him.

St. Athanasius [Orationes contra Arianos, Discourse III, Paragraph 34 (AD 356)]

As the Lord, putting on the body, became man, so we men are deified by the Word as being taken to Him through His flesh, and henceforward inherit life everlasting.

St. John of Damascus [De Fide Orthodoxa, Book II, Chapter 12]

God then made man without evil, upright, virtuous, free from pain and care, glorified with every virtue, adorned with all that is good, like a sort of second microcosm within the great world, another angel capable of worship, compound, surveying the visible creation and initiated into the mysteries of the realm of thought, king over the things of earth, but subject to a higher king, of the earth and of the heaven, temporal and eternal, belonging to the realm of sight and to the realm of thought, midway between greatness and lowliness, spirit and flesh: for he is spirit by grace, but flesh by overweening pride: spirit that he may abide and glorify his Benefactor, and flesh that he may suffer, and suffering may be admonished and disciplined when he prides himself in his greatness: here, that is, in the present life, his life is ordered as an animal's, but elsewhere, that is, in the age to come, he is changed and--to complete the mystery--becomes deified by merely inclining himself towards God; becoming deified, in the way of participating in the divine glory and not in that of a change into the divine being.

St. Gregory Nazianzen [Oration XXX, section 14: The 4th Theological Oration]

Even now, as man, Christ makes intercession for my salvation, for He still possesses the body which He assumed in order to make me God by virtue of His Incarnation.

St. Justin Martyr [The First Apology, Chapter XXI]

And we have learned that those only are deified who have lived near to God in holiness and virtue; and we believe that those who live wickedly and do not repent are punished in everlasting fire.