David Bradshaw: The Transformation of energeia into esse in the West

… how energeia as it is found in Plotinus and Porphyry was transformed into the medieval (and especially Thomistic) concept of esse, the ”act of being.” Tracing this history will reveal a major and relatively little noticed source of medieval thought. At the same time it will be important to notice what the developments we are tracing leave behind. At each stage there is a king of sloughing off of unwanted metaphysics. This is usually done silently, so that a reader not familiar with the earlier texts will be unaware of how key concepts have been removed from their original setting and radically simplified. [David Bradshaw, Aristotle East and West: Metaphysics and the Division of Christendom, 97]

In effect we find in [Marius - DHC] Victorinus a further specification of the energein katharon of the Anonymous Commentary [on Pamenides -DHC]. This energein now turns out to be esse, the unlimited and uncircumscribed being of the Father, from which is derived all the limited and circumscribed being (ὄν) found in the Son. Such esse is anything but “being” conceived as a static condition of existence; it is a kind of inwardly directed activity, containing implicitly life and intelligence as well as existence. In thinking itself it manifests itself as what it is, giving rise to the triad of ese, vivere, and intellegere – Father, Son and Holy Spirit. Oddly enough, then, despite all the accretions of Neoplatonism, we are not too far from the self-thinking thought of Aristotle’s Prime Mover. The divine self-intellection remains the activity par excellence, the one that precedes all others, giving rise by virtue of its necessary intrinsic structure to the intelligible order and plurality of the world. (Ibid., 115)

According to David Bradshaw's resarch, it seems that there is a shift in the West (after Plotinus) to turn activity into being, energeia into esse. This is troubling for many reasons, but it would answer the question of how pure act is interpreted in Classical Theism to be a rejection of divine choices and activity outside the being of God.