With all due respect, Father, I think you'll find that it was +Athanasius the Great who said that in "On the Incarnation".
The Eastern Fathers, as +Gregory Palamas points out, were uniform in their teaching that we do not come into a union with the Ουσια of our Triune God. Indeed, they also held that although we were created in the image and likeness of God, we cannot even actually "see" God.
"It is my opinion that our intellect does not have a natural power to be moved to the divine vision of Divinity. And in this one deficiency we are the peers of all the celestial natures, for both in us and in them grace moves that which is alien by nature both to the human intellect and to the angelic. For divine vision concerning the Godhead is not to be numbered among the other kinds of divine vision. For we possess divine vision of the natures of things through participation in their twofold nature, because there is a portion of all things in us. But we do not have a portion of the nature of the Divine Essence, and so neither do we have by nature divine vision of it." +Isaac the Syrian
What we can experience is the uncreated energy of God as a divine light, as the Apostles saw the light on Mt. Tabor at the Theophany. This energy "is" God, though not His essence. The Holy Spirit, we know, can take up a dwelling in us. So it seems that the Fathers teach that God enters us and through His grace transforms us. This is quite different from the popular, but pagan notion that the deification the Fathers speak of involves some sort of absorbtion into God, a sort of divine oblivion. I think that's one of the dangers with the idea that we come to share in the "Divine Nature".
"'Can a man take fire into his bosom, and his clothes not be burned?' (Prov. 6:27) says the wise Solomon. And I say: can he, who has in his heart the Divine fire of the Holy Spirit burning naked, not be set on fire, not shine and glitter and not take on the radiance of the Deity in the degree of his purification and penetration by fire? For penetration by fire follows upon purification of the heart, and again purification of the heart follows upon penetration by fire, that is, inasmuch as the heart is purified, so it receives Divine grace, and again inasmuch as it receives grace, so it is purified. When this is completed (that is, purification of heart and acquisition of grace have attained their fullness and perfection), through grace a man becomes wholly a god." +Symeon the New Theologian
and
"Moses and David, and whoever else became vessels of divine energy by laying aside the properties of their fallen nature, were inspired by the power of God... They became living ions of Christ, being the same as He is, by grace rather than by assimilation..." +Gregory Palamas
and
"The grace of deification thus transcends nature, virtue and knowledge, and (as St. Maximus says) `all these things are inferior to it.' Every virtue and imitation of God on our part indeed prepares those who practice them for divine union, but the mysterious union itself is effected by grace. It is through grace that `the entire Divinity comes to dwell in fullness in those deemed worth,' and all the saints in their entire being dwell in God, receiving God in His wholeness, and gaining no other reward for their ascent to Him than "God Himself." +Gregory Palamas
Anyway, its an important topic since it is definitional of what Eastern Christianity means when it speaks of "salvation" (theosis). Its rather different from popular Western Christian (not at all necessarily Latin Christian) notions about what, ultimately, it means to be "saved".
I trust you had a spiritually fruitful day, Father. Please pray for me at the Liturgy tomorrow.
St. Augustine did say it, it’s not a typo! And with him and St. Athanasius many others say the same in similar words. For St. John of the Cross it is “transforming union”, for St Teresa of Avila it is the “mystical marriage”, for Bl. Elizabeth of the Trinity it is especially the “indwelling Trinity”. In the end words escape even the saints at describing what God has prepared for those who love him.
Thank you for the many beautiful quotes. And yes, for most westerners (and I’m not referring to John Wayne!) “salvation” is thought of only in terms of sin. Not to keep referring to myself, but my vlog this week on AirMaria.com is specifically on salvation in the broader sense, a distinction that St. Irenaeus makes: salvation is not a synonym for redemption from sin.
God bless....