I think that there is a point being missed here. The contemplative tradition of the East certainly asserts that The God we experience in His activity is truly God. And yet there is also a progression of how we experience that God as we grow, such that as the mind is purified and grows it moves from contemplating God in his activity in history, to contemplating Him in a more essential way in creation, to contemplating Him in his essential powers, to contemplating Him to some degree in His unknowable essence. (This may not be exactly right, I don't have the quotes handy and am going by memory) Thus in our experience there is a distinction between experiencing God's presence/being in a fuller way and simply experiencing God in His activity.
Reid does not compare the Western and Eastern mystical traditions in his book, though he does discuss in length the critical importance of ascesis in the experience of God for both Florovsky and Lossky.
In chapter 2 Reid paraphrases Lossky's critique of the Western essentialist position, as it pertains to the vision of God. Can the saints in this life be given a vision of God in his essence? Apparently the Latin answer was yes. From the Western point of view, therefore, the Palamite distinction between essence and energies seemed to imply "a reduction or even a denial of the reality of the vision of God in mystical experience" (p. 52). "From the Eastern point of view," on the other hand, "the western position appeared to dissolve the proper distinction between theologia
. The western position seemed, on the face of it, to allow a more intimate relationship to God, viz., the face-to-face encounter with God's inner being. But what this actually meant, according to Lossky, was that western theology remained on the level of the energy (because the vision of God is of God's glory, not God's inner being), without itself being aware of its own deficiency. Western theology is incapable of grasping the idea that God is bigger than what is revealed of God--so Lossky argues. The apophatic method has no place in western theology except as a corrective against the supposition that human speech could describe the Godhead. If we use the concepts of 'essence' or 'being' we reach the limits of this western apophatic corrective, according to Lossky, because the attempt is made to describe God precisely in terms of these concepts. Western theology has no room for a concept of superessentiality" (p. 52).
The Palamite vision of God is, according to Lossky, no mere vision, no mere encounter with a two dimensional datum. This would in effect be an encounter with a "closed door." The doctrine of energies with its accompanying method of mystical praxis means that, on the contrary, a door is opened, an "infinite path beyond knowledge," and "existential communion." This stands in contrast to any mysticism in which God's glory is glimpsed face to face, and in which the beholder then rests satisfied because he or she mistakes this glory for the divine essence itself. The hesychast way, by contrast, sees the vision of glory as the beginning of an ever-deepening relationship of participation, a relationship that stretches beyond the limits of seeing and knowing. (p. 54)
One would think that Reid would probe Lossky's interpretation of the Western mystical tradition a bit further. I wonder if St Teresa of Avila would describe her experience of God as static. Is there no place for "growth" in the essentialist tradition? But Reid doesn't explore this question.
Reid does briefly compare Aquinas and Palamas in chapter 4. Both theologians are concerned to assert the vision of God and union with God, while at the same time protecting against the possibility of becoming God in his essence. He quotes Jurgen Kuhlmann:
We stand confronted by an apparent contradiction: Thomas made a differentiation between entitative and intentional participation (we will indeed see God's essence, but not become God's essence), while Palamas saw the two together (and therefore denied any vision of the essence). But now Palamas makes this other differentiation (knowledge is not the same as the vision of the [uncreated] light), but Thomas does not make this differentiation, rather declaring knowledge and the light to be one and the same.
Within the Latin scholastic tradition, theologians will thus speak of an intentional participation in the essence of God but refrain from speaking of an entitative participation, as that would imply the abolition of creaturehood and transformation into God in his essence. Within the Eastern tradition, theologians will speak of an entitative participation in the divine energies, but they refrain from speaking of a vision of the divine essence, as that would imply becoming an hypostasis in the Godhead.
Reid notes one way Lossky's critique does accurately touch the Western tradition: for both Aquinas and Rahner, seeing or not seeing God is definitive: we either see God or we do not. Similarly for Barth, we either hear God or we do not. "There is no question here of a growth or a progress in the relationship," writes Reid. "There is only the question of the either/or. Either we see/hear, or we fail to" (p. 71). But Reid rejects Lossky's claim that the western tradition remains on the level of the energies. "The very terms in which this critique is phrased, which assume different levels within the Godhead, is simply not the language of western theology" (p. 71). Moreover, one might even argue that the Western understanding of intentional participation in the divine essence offers even a fuller understanding of the Christian experience of God:
To some extent with have to agree [with Lossky]. "Intentional" participation without "entitative" participation is indeed something less than full participation. Barth's doctrine of reconciliation is indeed less ambitious than the "maximalism" of Lossky's doctrine of deification. At the same time, however, we have to notice that Lossky does not aim at entitative participation in the divine essence. It would be equally possible to argue that the claim to a vision of the divine essence is more "maximal" than a claim to a vision of God's glory. But the argument would be just as futile as the original critique. Both theologies use separate terminologies and make different distinctions. Both, however, seek to safeguard the same underlying intention--to praise God as the trinity, to regard human beings as beloved creatures of God, and to deepen the human relationship with God. (p. 72)
I am surprised that Reid does not discuss Rahner's understanding of the Beatific Vision and would judge this to be a serious weakness of his book. Of course, the Beatific Vision has no place in the theology of Karl Barth.