In biblical history the Lord gives us, not only the definitive revelation of Himself but also the conclusive revelation of man. That is to say, divine revelation addresses not only the question, "Who is God?" but also the question, "What is man?" I suggest it is useful for Christians to reflect on the unique character of the Bible's answer to this question, because we take our biblical anthropology so much for granted that we fail to count it among those things that many prophets and kings have desired to see but have not seen them.Fr. Reardon goes on to make a case for the Eastern Orthodox doctrine of 'theosis' (deification), which is not quite what it may sound like it is. It is the thoroughly Christian and Catholic doctrine, really, of human nature becoming transformed in Christ by being incorportated into Christ and conformed to His divinity. The notion is attested in 2 Peter 1:4, where St. Peter speaks of our becoming "partakers of the divine nature." This is what Fr. Reardon intends by his argument above, and with this we have no quarrel.
Without divine revelation there are all sorts of theories about man, and in fact the Christian Gospel was obliged to contend with certain of those theories.
One such theory, for instance, claimed (and still does) that "human nature does not change." This theory is understandably attractive, because it provides a sense of universality among human beings and a sense of continuity throughout history. Indeed, as applied to a specified, narrow range of human experiences, we can even call it true.
Yet, if we adhere to the full anthropology of divine revelation, it is strictly speaking not true that "human nature does not change." Indeed, it is the very business of divine revelation to cause human nature to change.
However, I propose a caveat to Fr. Reardon's notion here of an 'unfixed' human nature above, because it think it is open to serious, if unintended, misunderstandings and distortions. With all due respect to the vitally imperative point that Fr. Reardon is making here about the Athanasian thesis that God became man in order to make men 'divine,' one can easily see even in stating the matter thus how easily it can fall prey to misunderstanding. God did become man in Jesus. But when men are elevated in theosis to become "partakers of the divine nature" (as St. Peter says in his epistle), they do not cease being creatures or cease belonging to the species, homo sapiens. Reardon's point that human nature has a supernatural telos or end is important, but it must be supplemented by the addendum that this telos is always proper to the human nature or esse (he doesn't like that word, but there's neither anything objectionable about it, nor is the concept it entails avoidable). As human nature has natural ends (physical and social wellbeing, marriage, children, etc.), so it has supernatural ends (sanctity, glorification, and eternal fellowship with the Holy Trinity). But while these supernatural ends are proper to a nature that is altered by the remediating sanctifcation of God's grace, they are also ends that are proper to a human nature. They are not ends proper to, say, the nature of a stone, a tree, a cloud, or a tadpole. Thus, while I would second Fr. Reardon's notion of theosis as involving human nature in an openness to change, I would not want anyone to mistakenly suppose this notion of 'change' to mean that human beings have no stable nature -- a currently quite popular view among those who presume, among other things, that same-sex 'marriage' may substitute for the heterosexual archetype among men and women with 'changed' natures.
Fr. Reardon is a friend of mine. We have sat on the same panels at conferences. I know him and like him, and we find ourselves on the same side of many arguments, even if we disagree on the 'little' matter of the Papacy and Church authority. I consider him a great ally in the culture wars that beset us, just as I number among some of my fellow Catholics those who would regard me as their enemy.