The term originally was used in Greco-Roman pagan society to venerate a ruler. It was inconceivable to Jewish piety. Yet, with a time, it was adopted in Eastern Christianity by the Greek Fathers to describe spiritual transformation of a Christian. The change of human nature was understood by them as a consequence of a baptized person being incorporated into the Church as the Body of Christ. Divinization was thus developed within the context of incarnational theology. The teaching about deification of a Christian can be found as early as in the works of Irenaeus, a Greek Father who was a head of the church of Lyons (c. 130–202) e.g. in the preface to his Adversus Haereses vol. 5. Athanasius of Alexandria was an author of the phrase about Jesus Christ which has become popular in Christmas homilies: "He was made human so that he might make us gods" (De incarnatione 54,3, cf. Contra Arianos 1.39). Divinization in the context of the Eucharist was taught by Gregory of Nyssa and Cyril of Alexandria. The term never meant for them breaching the absolute ontological distinction between God and his creation.
There were many different references to divinization in the writings of the Church Fathers.
In the second century, Irenaeus, bishop of Lyons (c. 130–202) said that God had "become what we are, that He might bring us to be even what He is Himself." He added:
Do we cast blame on him [God] because we were not made gods from the beginning, but were at first created merely as men, and then later as gods? Although God has adopted this course out of his pure benevolence, that no one may charge him with discrimination or stinginess, he declares, "I have said, Ye are gods; and all of you are sons of the Most High." ... For it was necessary at first that nature be exhibited, then after that what was mortal would be conquered and swallowed up in immortality.
At about the same time, Clement of Alexandria (c. 150–215), wrote: "Yea, I say, the Word of God became a man so that you might learn from a man how to become a god." Clement further stated that "[i]f one knows himself, he will know God, and knowing God will become like God. . . . His is beauty, true beauty, for it is God, and that man becomes a god, since God wills it. So Heraclitus was right when he said, 'Men are gods, and gods are men.'" Clement of Alexandria also stated that "he who obeys the Lord and follows the prophecy given through him ... becomes a god while still moving about in the flesh."
Justin Martyr c. 100–165) insisted that in the beginning men "were made like God, free from suffering and death," and that they are thus "deemed worthy of becoming gods and of having power to become sons of the highest."
Athanasius, bishop of Alexandria (c. 296–373), stated his belief in literal deification: "The Word was made flesh in order that we might be made gods. ... Just as the Lord, putting on the body, became a man, so also we men are both deified through his flesh, and henceforth inherit everlasting life." Athanasius also observed: "For the Son of God became man so that we might become God."
Augustine of Hippo (354–430) said: "But he himself that justifies also deifies, for by justifying he makes sons of God. 'For he has given them power to become the sons of God' [referring to John 1:12]. If then we have been made sons of god, we have also been made gods." "To make human beings gods," Augustine said, "He was made man who was God" (sermon 192.1.1). Augustine goes on to write that "[they] are not born of His Substance, that they should be the same as He, but that by favour they should come to Him... (Ibid)".
Other references to divinization in the writings of the Church Fathers include the following:
- Irenaeus (c. 130-200)
- "[T]he Word of God, our Lord Jesus Christ, who did, through His transcendent love, become what we are, that He might bring us to be even what He is Himself."[Primary 2]
- "'For we cast blame upon [God], because we have not been made gods from the beginning, but at first merely men, then at length gods; although God has adopted this course out of His pure benevolence, that no one may impute to Him invidiousness or grudgingness he declares, "I have said, Ye are gods; and all of you are sons of the Most High." "[Primary 3]
- "For it was necessary, at first, that nature should be exhibited; then, after that, that what was mortal should be conquered and swallowed up by immortality, and the corruptible by incorruptibility, and that man should be made after the image and likeness of God."[Primary 3]
- Clement of Alexandria (c. 150-215)
- "[T]he Word of God became man, that thou mayest learn from man how man may become God."[Primary 4]
- "For if one knows himself, he will know God; and knowing God, he will be made like God"[Primary 5]
- "[H]is is beauty, the true beauty, for it is God; and that man becomes God, since God so wills. Heraclitus, then, rightly said, "Men are gods, and gods are men." For the Word Himself is the manifest mystery: God in man, and man God"[Primary 5]
- "[H]e who listens to the Lord, and follows the prophecy given by Him, will be formed perfectly in the likeness of the teacher—made a god going about in flesh."[Primary 6]
- "And to be incorruptible is to participate in divinity..."[Primary 7]
- Justin Martyr (c. 100-165)
- "[Men] were made like God, free from suffering and death, provided that they kept His commandments, and were deemed deserving of the name of His sons, and yet they, becoming like Adam and Eve, work out death for themselves; let the interpretation of the Psalm be held just as you wish, yet thereby it is demonstrated that all men are deemed worthy of becoming "gods," and of having power to become sons of the Highest."[Primary 8]
- Theophilus of Antioch (c. 120-190)
- "For if He had made him immortal from the beginning, He would have made him God. Again, if He had made him mortal, God would seem to be the cause of his death. Neither, then, immortal nor yet mortal did He make him, but, as we have said above, capable of both; so that if he should incline to the things of immortality, keeping the commandment of God, he should receive as reward from Him immortality, and should become God..."[Primary 9]
- Hippolytus of Rome (c. 170-235)
- "And you shall be a companion of the Deity, and a co-heir with Christ, no longer enslaved by lusts or passions, and never again wasted by disease. For you have become God: for whatever sufferings you underwent while being a man, these He gave to you, because you were of mortal mould, but whatever it is consistent with God to impart, these God has promised to bestow upon you, because you have been deified, and begotten unto immortality."[Primary 10]
- "If, therefore, man has become immortal, he will also be God. And if he is made God by water and the Holy Spirit after the regeneration of the laver he is found to be also joint-heir with Christ after the resurrection from the dead."[Primary 11]
- Athanasius of Alexandria (c. 296-373)
- "Therefore He was not man, and then became God, but He was God, and then became man, and that to deify us"[Primary 12]
- "for 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."[Primary 13]
- "For He was made man that we might be made God."[Primary 14]
- Gregory of Nyssa (c. 335-395)
- "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 disseminated Himself in every believer."[Primary 15]
- "For just as He in Himself assimilated His own human nature to the power of the Godhead, being a part of the common nature, but not being subject to the inclination to sin which is in that nature (for it says: "He did no sin, nor was deceit found in his mouth), so, also, will He lead each person to union with the Godhead if they do nothing unworthy of union with the Divine."[Primary 16]
- Augustine of Hippo (c. 354-430)
- "'For He hath given them power to become the sons of God.'[John 1:12] If we have been made sons of God, we have also been made gods."[Primary 17]
- Maximus the Confessor
- "Nothing in theosis is the product of human nature, for nature cannot comprehend God. It is only the mercy of God that has the capacity to endow theosis unto the existing... In theosis, man (the image of God) becomes likened to God, he rejoices in all the plenitude that does not belong to him by nature, because the grace of the Spirit triumphs within him, and because God acts in him."
- Cyril of Alexandria
- "For we too are sons and gods by grace, and we have surely been brought to this wonderful and supernatural dignity since we have the Only Begotten Word of God dwelling within us."
- Gregory of Nazianzus
- implores humankind to "become gods for (God's) sake, since (God) became man for our sake."
- Likewise, he argues that the mediator "pleads even now as Man for my salvation; for He continues to wear the Body which He assumed, until He make me God by the power of His Incarnation." 
- "Through the medium of the mind he had dealings with the flesh, being made that God on earth, which is Man: Man and God blended. They became a single whole, the stronger side predominating, in order that I might be made God to the same extent that he was made man."
- Basil of Caesarea stated that "becoming a god is the highest goal of all"