To return to the question of the original poster: both the Catholic and Orthodox construals of grace are attempts to state in words a mystery that cannot be captured in words--namely, our participation by grace in the infinite life of the Father, Son, and Holy Spirit. The Orthodox theologian seeks to express this mystery by making a distinction within God between his imparticipable essence and his participable energies. The Catholic theologian seeks to express this mystery by making a distinction between uncreated grace and created grace. But both theologians agree completely that, by grace, we are truly given to share in the divine nature and participate in God through the Son by the Holy Spirit.
For my part, such an agreement is more than sufficient, but theologians, being theologians, like to push these questions to the nth degree. An example is the famous conversation between Eric Mascall and Vladimir Lossky, fictionalized in Mascall's book Via Media. Eric Mascall briefly compares the Thomist understanding of grace with the Palamite understanding. "For the Thomist," Mascall writes, "grace means a communication of the Creator to the creature in the created mode under which alone a creature can receive anything; for the Palamite, it means a communication of the uncreated energy of God, though not of his incommunicable essence." Mascall then offers a conversation between a Thomist and a Palamite based on a conversation between Lossky and Mascall hiimself:
Palamite: "You make no distinction between the essence of God and his energy and you say that God gives himself to the creature in a finite mode. On your showing, this must mean that the divine essence is given in a finite mode, and this is plainly impossible. Either what is given is finite, in which case it cannot be God, or what is given is God, in which case it cannot be given finitely. In the former case there is no real deification of man; in the latter case man ceases to be a creature. Neither alternative is admissible, so your theory must be false."
Thomist: "The whole matter is, of course, a profound mystery, but you have not been fair to my thought. I did not mean that God-in-a-finite-mode was given to the creature, but that God was received by the creature in a finite mode. The finitude is in the mode of participation, not in the object participated. And here is a dilemma for you, in return for that on which you tried to impale me. You say that the creature participates in the divine energy, though not in the divine essence. Now listen. Either the energy and the essence are identical, or else in participating in the energy the creature does not really participate in God. In the former case your own theory is false, in the latter it fails to provide for a real deification of man."
Palamite: "No, now it is you who are being unfair to me. The energy is divine, and therefore in participating in the divine energy the creature participates in God. God is present, really present, in his energy as much as in his essence. The only difference is that the energy is communicable and the essence is not. Thus God is really communicated in his energy, though he remains incommunicable in his essence."
Thomist: "Really, this is intolerable. God and his essence cannot be separated. If the energy communicates God it communicates his essence. And then you need my theory to explain how the creature can participate in God without losing its creatureliness."
I suggest that the Eastern and Western theologians are asking different questions. The Eastern theologian asks, "How is it that God can truly communicate God to creatures?" He answers this question by positing a distinction within God between his imparticipable essence and his participable energies. His answer is theological. The Western theologian, particularly within the scholastic tradition, asks, "How is it possible for the human creature to receive deity? In what ways must he be transformed and altered to make this supernatural union possible?" He answers this question by invoking a distinction between uncreated and created grace. His answer is metaphysical.
The classic Eastern concern is to insist that the human creature, by the gift of grace, truly participates in divinity. The classic Western concern is insist that participation in God does not obliterate human nature but rather sanctifies and transforms it. These concerns are not incompatible, even though the Orthodox and Catholic theologian typically reflect upon the mystery of divine union through different conceptualities. Orthodox and Catholic are united in their common conviction that in his unmerited love God communicates himself to sinners and incorporates them into the mystery of his Trinitarian life.