St. Hilary of Poitiers [De Trinitate: Book IX, Paragraph 4]
It was God alone Who could become something other than before, and yet not cease to be what He had ever been; Who could shrink within the limits of womb, cradle, and infancy, yet not depart from the power of God. This is a mystery, not for Himself, but for us. The assumption of our nature was no advancement for God, but His willingness to lower Himself is our promotion, for He did not resign His divinity but conferred divinity on man.
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.
St. Gregory Nazianzen [Oration XL, section 45: The Oration on Holy Baptism]
Believe that the Son of God, the Eternal Word, who was begotten of the Father before all time and without body, was in these latter days for your sake made also Son of Man, born of the Virgin Mary ineffably and stainlessly (for nothing can be stained where God is), and by which salvation comes, in His own Person at once perfect Man and perfect God, for the sake of the entire sufferer, that He may bestow salvation on your whole being, having destroyed the whole condemnation of your sins: impassible in His Godhead, passible in that which He assumed; as much Man for your sake as you are made God for His.
St. Augustine, Bishop of Hippo [Psalm 50, sections 1-2]
For as he saith in this Psalm, not any man whatever nor any angel whatever, but, "The Lord, the God of gods, hath spoken" (ver. 1). But in speaking, He hath done what? "He hath called the earth from the rising of the sun unto the going down." He that "hath called the world from the rising of the sun unto the going down," is Our Lord and Saviour Jesus Christ, "the Word made Flesh," in order that He might dwell in us. Our Lord Jesus Christ then is the "God of gods;" because by Himself were all things made, and without Himself was nothing made. The Word of God, if He is God, is truly the God of gods; but whether He be God the Gospel answereth, "In the beginning was the Word, and the Word was with God, and the Word was God." And if all things were made by Himself, as He saith in the sequel, then if any were made gods, by Himself were they made. For the one God was not made, and He is Himself alone truly God. But Himself the only God, Father and Son and Holy Ghost, is one God.
But then who are those gods, or where are they, of whom God is the true God? Another Psalm saith, "God hath stood in the synagogue of gods, but in the midst He judgeth gods." As yet we know not whether perchance any gods be congregated in heaven, and in their congregation, for this is "in the synagogue," God hath stood to judge. See in the same Psalm those to whom he saith, "I have said, Ye are gods, and children of the Highest all; but ye shall die like men, and fall like one of the princes." It is evident then, that He hath called men gods, that are deified of His Grace, not born of His Substance. For He doth justify, who is just through His own self, and not of another; and He doth deify who is God through Himself, not by the partaking of another. But He that justifieth doth Himself deify, in that by justifying He doth make sons of God. "For He hath given them power to become the sons of God." If we have been made sons of God, we have also been made gods: but this is the effect of Grace adopting, not of nature generating. For the only Son of God, God, and one God with the Father, Our Lord and Saviour Jesus Christ, was in the beginning the Word, and the Word with God, the Word God. The rest that are made gods, are made by His own Grace, are not born of His Substance, that they should be the same as He, but that by favour they should come to Him, and be fellow-heirs with Christ. For so great is the love in Him the Heir, that He hath willed to have fellow-heirs.
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. Basil the Great [On the Holy Spirit, Chapter 9]
From the Spirit comes foreknowledge of the future, understanding of the mysteries of faith, insight into the hidden meaning of Scripture, and other special gifts. Through the Spirit we become citizens of heaven, we are admitted to the company of the angels, we enter into eternal happiness, and abide in God. Through the Spirit we acquire a likeness to God; indeed, we attain what is beyond our most sublime aspirations -- we become God.
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. Augustine [Sermon 13]
Beloved, our Lord Jesus Christ, the eternal Creator of all things, today became our Savior by being born of a mother. Of His own will He was born for us today, in time, so that He could lead us to His Father's eternity. God became man so that man might become God. The Lord of the angels became man today so that man could eat the bread of angels."
St. Hippolytus [On the Refutation of All Heresies]
When we have come to know the true God, both our bodies and our souls will be immortal and incorruptible. We shall enter the kingdom of heaven, because while we lived on earth we acknowledged heaven's King. Friends of God and coheirs with Christ, we shall be subject to no evil desires or inclinations, or to any affliction of body or soul, for we shall have become divine. It was because of our human condition that God allowed us to endure these things, but when we have been deified and made immortal, God has promised us a share in his own attributes.
St. John of Damascus [De Fide Orthodoxa, Book IV, Chapter 13]
Man, however, being endowed with reason and free will, received the power of continuous union with God through his own choice, if indeed he should abide in goodness, that is in obedience to his Maker. Since, however, he transgressed the command of his Creator and became liable to death and corruption, the Creator and Maker of our race, because of His bowels of compassion, took on our likeness, becoming man in all things but without sin, and was united to our nature. For since He bestowed on us His own image and His own spirit and we did not keep them safe, He took Himself a share in our poor and weak nature, in order that He might cleanse us and make us incorruptible, and establish us once more as partakers of His divinity.
For it was fitting that not only the first-fruits of our nature should partake in the higher good but every man who wished it, and that a second birth should take place and that the nourishment should be new and suitable to the birth and thus the measure of perfection be attained. Through His birth, that is, His incarnation, and baptism and passion and resurrection, He delivered our nature from the sin of our first parent and death and corruption, and became the first-fruits of the resurrection, and made Himself the way and image and pattern, in order that we, too, following in His footsteps, may become by adoption what He is Himself by nature, sons and heirs of God and joint heirs with Him. He gave us therefore, as I said, a second birth in order that, just as we who are born of Adam are in his image and are the heirs of the curse and corruption, so also being born of Him we may be in His likeness and heirs of His incorruption and blessing and glory.
St. Hilary of Poitiers [De Trinitate: Book IX, Paragraph 38]
The Incarnation is summed up in this, that the whole Son, that is, His manhood as well as His divinity, was permitted by the Father's gracious favor to continue in the unity of the Father's nature, and retained not only the powers of the divine nature, but also that nature's self. For the object to be gained was that man might become God.