The Eastern view of theosis (at least from Gregory Palamas and on) has at its heart the “incommunicable ESSENCE” of God. This essence is absolutely beyond the ability to experience, enter into, … for the human. It is God’s ENERGIES that are completely part of the deified human, but the essence if forever beyond.
This is at odds with Thomist views which claim that the beautific vision consists of God’s essence and energies not merely His energies.
If it matters, here is a section from David Bradshaw in Aristotle East and West: Metaphysics and the Division of Christendom, pages 255-256:
Aquinas’ teaching on the beatific vision exhibits with particular clarity the difference separating him from the eastern tradition. The most immediately obvious is that, whereas for the East God is beyond knowing, Aquinas regards Him as the highest intelligible object. Aquinas is aware of this disagreement. In the De Veritate he cites a long string of objections to the possibility of seeing God through His essence, and among them are several drawn from Dionysius and John of Damascus. The most fundamental, which Aquinas attributes to Dionysius, is that “all cognition is of things that are; God, however, is no a being, but is above being; therefore, He cannot be known except by transcendent knowledge, which is divine knowledge.” Aquinas’ reply is worth quoting in full:
“Dionysius’ argument proceeds from the knowledge had while in this life. This is had from forms in existing creatures, and, consequently, it cannot attain to what is transcendent. Such is not the case, however, of the vision had in heaven. His argument, therefore, is not pertinent to the problem at hand.”
What for Dionysius had been a limitation inherent to the relation between creature and Creator become for Aquinas one imposed solely by our current ways of knowing. It is worth noting that Aquinas’ position had been considered and rejected by St. Gregory of Nyssa. In his Contra Eunomium Gregory denies that the ousia of God is known even to the angels, precisely in order to insist that this limitation is not due solely to human ways of knowing but is an intrinsic limitation of the creature. Gregory’s writings were not available to Aquinas, however, and even if they had been it is unlikely that Aquinas would have changed his mind. He notes at the beginning of this article of the De Veritate that the denial that God can be seen through His essence had already been judged heretical. This judgment occurred at the University of Paris in 1241, in the rejection of the proposition that “the divine essence will be seen in itself neither by man nor by angel.” In his Commentary on Hebrews Aquinas attributes the rejected view to Eriugena, who in turn (unknown to Aquinas) depended for this point on St. Maximus the Confessor. One could hardly find a more string example of the misunderstanding between the two halves of Christendom: a view that Aquinas regards as heretical had, unknown to him, been orthodox in the East since at least the fourth century.
This is tangentially related to the material / immaterial discussion already mentioned, but it really goes much deeper. I do not believe firm dogmatism exists on either side, but things like the Filioque clause are related and there is a lot of dogmatism concerning this of course.
If it is not obvious from the above I think the idea of deification in Aquinas’ thought is closer to the idea I espouse as a LDS than is the idea of Palamas. My experience with most Western Christians is after they come to grips with what is quite universally taught concerning “men can become gods” they immediately borrow from centuries of Eastern Orthodox understanding without recognizing that there are some foundational conflicts they have overlooked.
I will say however, for my part of it I do not think Eastern, Western, or LDS Christians (myself) included have such a perfect understanding of what it is to become gods that such distinctions should be points that are so filled with vilification for the others views (which doesn’t stop me from being all too convinced that my LDS understanding is more true and more in line with the ECF than the other understandings …. )