Peter Leithart on Theopoiesis.
Discussion at Sacramentum Vitae.Carl Mosser of Eastern College gave a superb presentation on deification at the ETS meeting. A large part of the presentation was a study of terminology. He noted that the Greek work THEOS (often thought to be equivalent to "God") had a broader meaning, referring to powers that were immortal, incorruptible, and glorious - the very words that Paul uses in 1 Corinthians 15 to describe the resurrected body. For the early fathers, this is what is meant by "deification," and they frequently link the doctrine to adoption via Psalm 82. Deification is not a capitulation to Hellenism (as Harnack argued) but grew out of biblical exegesis and the patristic understanding of salvation. (Interestingly, Mosser said that 2 Peter 1:4 plays little role in the earliest fathers.)
Gregory of Nazianzus was the first to use the word "theosis" to describe this, and he used it very infrequently. The doctrine and terminology of theosis kicks into gear with Pseudo-Dionysus, the hesychast controversy, Palamas and Maximus the confessor. It is thus linguistically anachronistic to claim that the early fathers have a doctrine of "theosis." With the hesychast controversy, not only the terminology but the doctrine changes. Instead of a strongly soteriological understanding of deification, theosis develops in a mystical context, and is worked out by Palamas and others through the distinction between the essence and energies of God, a distinction that has no place in the earliest doctrine of deification.
The confusion of theosis and the broader doctrine of deification creates significant ecumenical problems. Deification is an ecumenical doctrine, taught in some form by everyone from Irenaeus to Wesley and beyond, but theosis is a distinctly Orthodox development. When the two are confused, deification appears to be a distinctly Orthodox teaching as well. Treating the two as synonymous also leads ecumenically minded Western theologians to downplay the distinctiveness of mystical theosis; Eastern apologists, meanwhile, claim that a true doctrine of deification must take the uniquely Eastern form - complete with the essence/energies distinction - and when the West is found to lack such a teaching, Eastern apologists can claim that the West lacks a doctrine of deification as such.
Mosser ended with some consideration of the best way to describe the reality of deification. The term raises problems, since it implies that men become deities; divinization is hardly better. Mosser suggested that "theopoiesis" is the best way to describe the general, ecumenical view of the church, of which theosis is a uniquely Orthodox variation.