Early Church verses and quotations on theosis (θέωσις)

Theosis (Greek θέωσις), meaning "deification" or "divinization", is the mystical doctrine that "God became man, so that man might become God" (St. Athanasius, 4th century, On the Incarnation 54:3). We are to be united to Christ, becoming Christ ourselves in humility, not in essence but by grace. We are all meant to be shining lamps of God's love. 

This doctrine is found in scripture, and in early Christian literature such as the mystical Odes of Solomon in the 1st century, in the apocryphal Gospel of Thomas in the 1st-3rd century, and in the beautiful "Hymn of the Pearl" in the 1st-2nd century. The doctrine is also found in the writings of Origen in the 3rd century and the brilliant writings of St. Maximos the Confessor in the 7th century.

The belief—that man is to "become God" in a sense—is also found at the very beginning of scripture, in Genesis 1, where man is made "in the icon [image] of God" and given dominion over "all the earth" (Genesis 1:26-27). 

The doctrine of theosis is central to the Eastern Orthodox Church, and sums up Her view of salvation and the goal of Christian life. Theosis is expressed in many places in early Christian literature: 

I have been crucified with Christ; it is no longer I who live, but Christ lives in me... (Galatians 2:20) 

He who overcomes, I will make him a pillar in the temple of My God, and he shall go out no more. I will write on him the name of My God and the name of the city of My God, the New Jerusalem, which comes down out of heaven from My God. And I will write on him My new name. (Apocalypse 3:12)

It is not uncommon that the pillars in Orthodox churches depict icons of the saints. So to become "a pillar in the temple of My God" is to be among the saints. To bear Christ's "new name" is to be Christ—to realize fully the icon of Christ within oneself. Surely we are all so far from the goal! We all fall short of Christ. But we strive onwards.

Behold, I stand at the door and knock. If anyone hears My voice and opens the door, I will come in to him and dine with him, and he with Me. To him who overcomes I will grant to sit with Me on My throne, as I also overcame and sat down with My Father on His throne. (Apocalypse 3:20-21)

So we are told in St. John's Apocalypse, in scripture, that the victorious Christian is meant to sit with Christ on His throne. 

The doctrine is also found outside of scripture in very early texts. The Odes of Solomon, written by a 1st-century Jewish Christian, for example: 

I have been united to Him, for the Lover has found the Beloved, And because I shall love Him that is the Son, I shall become a son. For he that is joined to Him that is immortal, will also himself become immortal; and he who has pleasure in the Living One, will become living. (Odes of Solomon 3:8-11)

The Spirit brought me forth before the face of the Lord; and, although a son of man, I was named the Illuminate, the Son of God... (Odes of Solomon 36:3)

The mysterious author both speaks of Christ as distinct from himself and as though he were Christ himself.

The Gospel of Thomas (though it is a proto-Gnostic text) echoes the phrase "I will write on him My new name" of Apocalypse 3:12 and echoes the verse John 4:14 about drinking the living water given by Christ: 

Jesus said, "He who will drink from my mouth will become like Me. I myself shall become he, and the things that are hidden will be revealed to him." (Gospel of Thomas 108)

And the ancient "Hymn of the Pearl" is a poem reflecting the journey of the Christian, who is lost in the world and enslaved by sin (represented by Egypt), and is called out of the world, and welcomed home as a child of God:

You shall put on your robe, And your mantle that goes upon it, And with your Brother, Our Second, You shall be heir in Our kingdom. ("The Hymn of the Pearl", Acts of Thomas)

I remembered that I was a son of royal parents, and my noble birth asserted itself. (ibid.)

The author speaks of being an heir in the kingdom of God, and of being a son of God.

Origen, the great Christian writer of the 3rd century, had the following to say, referring to the foot of the Cross in John 19:26:

Is it not the case that every one who is perfect lives himself no longer, but Christ lives in him? And if Christ lives in him, then it is said of him to Mary, ‘Behold your son Christ.' (Commentary on John, Book 1, Ch. 6)

Origen, exemplary of early Christian belief, plainly interprets this verse of John in terms of theosis. 

Moreover, St. Maximos the Confessor has the following to say regarding theosis: 

[T]hose who choose the pure and undefiled life of the Gospel ... become living icons of Christ, or rather become one with Him through grace (rather than being a mere simulacrum), or even, perhaps, become the Lord Himself, if such an idea is not too onerous for some to bear. (St. Maximos the Confessor, Ambigua 20:2)

The function of mystical theology is by grace to make the mind (νοῦς) like God and equal to Him—as far as this is possible—so that it becomes totally unaware, because of its transcendent state, of anything that is sequent to God. (Various Texts on Theology, the Divine Economy, and Virtue and Vice, 5:94, Philokalia)

St. Maximos says "[they] become the Lord Himself" even as Christ in the Gospel of Thomas says "[they] will become like Me. I myself shall become [them]."

Theosis is connected to all ancient Christian practices, including veneration of saints, veneration of Mary the Mother of God, and icons. This is because a saint who acquires theosis shines forth with the light of God as a true icon of Christ. To venerate the saint, or the icon of the saint, is thus to give honor to the icon of God, and therefore to honor God; for "the honor paid to the icon passes on to the prototype", as St. Basil says in the 4th century (The Holy Spirit, Ch. 18, 45). And when the saint is glorified with grace and miracles, God is glorified through that saint. The ancient Church gives glory to God by venerating His saints and their icons. It is God's good pleasure that we do so; God created man so that He could clothe man in His glory. That the saints are venerated does not take away glory from God, but is another way of giving honor and glory to Him, since God dwells in the saints.

Theosis is also connected to the Eucharist—the focal point of Christian worship. When one consumes the body and blood of Christ, one is transformed into Christ. How can this not be so? It is said, "You are what you eat". And what you drink enters into your bloodstream, so that it is Christ's own blood which now courses through the veins of one who communes at the Chalice. 

It is the aim of the Christian to enter into marriage with God, to be wed to Him, and united to Him as the Son to the Father and as the Bride to the Bridegroom, in a relationship that reflects the Holy Trinity. From this love, light will pour forth into the world, and the Christian will shine as Christ did, with "grace and truth" (John 1:14, 1:17).

It cannot be disputed that theosis is truly a doctrine of the early and ancient Church—one that was expressed by the Apostles themselves in scripture. The modern churches of the West do not put such emphasis on this doctrine (apart from Protestant notions of "sanctification"). But the true Church has always emphasized salvation as a mystical union with Christ and with God—even to the extent of "becoming" Christ Himself, "if" (in the words of St. Maximos) "it is not too onerous for some to bear".