Over the next several days, medicine I am doing a series on Gregory of Nyssa and his doctrine of perfection as found in two of his writings: The Life of Moses, and On Perfection. The introductory post can be found here.
Part of the difficulty when looking at Gregory of Nyssa’s doctrine of perfection is determining what contemporary theological words should be used to describe his doctrine. Is he talking about sanctification, or theosis, or both? Some current Eastern Orthodox theologians make a strong distinction between sanctification and theosis, suggesting that the terms cannot be used synonymously. On the other hand, Brother Casimir chooses to use the term sanctification, rather than theosis to describe the theology in On Perfection. Michael Gorman’s definition of theosis sounds like a solid definition of sanctification: “Theosis is transformative participation in the kenotic, cruciform character of God through Spirit-enabled conformity to the incarnate, crucified, and resurrected/glorified Christ.” Ivan Popov suggests that perfection (or sanctification) is the moral element of theosis.
I would suggest that, given that Gregory is working without developed theological systems, and, as will be seen, is the pioneer in the idea of perfection being found in change and not in stability, that Gregory’s doctrine of perfection encompasses both sanctification and glorification (theosis), and not necessarily in a progressive (sanctification leads to theosis) order. This is because, even though Gregory follows the events of Moses’ life, for example, in a chronological order, he does not absolutize this order into a “schematized progression of spiritual experience.” As will be seen, because Gregory advocates for a perpetual growth that has no end, I would suggest that the term ‘perfection’ encompasses both sanctification and theosis; it is both a process that happens now and at the same time it is never-ending. For the sake of uniformity, I will endeavour to use the term “perfection” rather than sanctification or theosis.
 Vladimir Kharlamov, “Introduction” in Stephen Finlan and Vladimir Kharlamov, eds., Theosis: Deification in Christian Theology (Eugene: Pickwick Publications, 2006), 5.
 Brother Casimir, “Saint Gregory of Nyssa: ???? ??????????? – On Perfection,” 349. References to the actual text of “On Perfection” will be cited as OP section (e.g., OP J.213)
 Michael Gorman, Inhabiting the Cruciform God: Kenosis, Justification and Theosis in Paul’s Narrative Soteriology (Grand: William B. Eerdmans Publishing, 2009), 7.
 Ivan Popov, “The Idea of Deification in the Early Eastern Church,” in Theosis: Deification in Christian Theology, ed. Vladimir Kharlamov, vol. 2 (Eugene: Pickwick Publications, 2011), 64.
 Gregory of Nyssa, The Life of Moses, 13. References to the actual text of The Life of Moses will be cited as LoM book, section (e.g., LoM II, 118).