It is Not Good that Man Should be Allone
In purely abstract terms, person is covariant with centration. De Lubac illuminates this aspect of the problem:
"[W]e find that the higher a living thing rises in the scale of being, the more internal unity does it acquire." In contrast, "the undifferentiated, entirely homogeneous being is as little one as it is possible to be." Rather, the latter "is only a nameless agglomeration."
Therefore, the first thing we need to understand is that one -- or oneness, rather -- is located at the top of of the scale, not the bottom.
The infant, for example, when he is fed, dry, and comforted, is presumably "at one" with the cosmos. But this represents a very simple, or shallow, degree of oneness. As human beings grow and acquire more "parts," it becomes increasingly difficult to pull off oneness while retaining the achievement of identity.
De Lubac notes that in certain plants, "unity is so weak that every piece cut from the stalk produces a new plant." Each part is its own potential whole, so to speak.
The inverse obtains in something as complex as a human being, where each part supports the unity of the whole. A tooth is quite different from a toe, but each has its specific role to play.
Likewise, unlike earthworms, you can't cut someone in half and expect each half to grow into a separate person (unless the division happens during the very early and undifferentiated blastocyst stage).
Transposed to the psychic level, "True union does not tend to dissolve into one another the beings that it brings together, but to bring them to completion by means of one another. The Whole, therefore, is not the antipodes, but the very pole of personality" (ibid).
Thus, two errors need to be dispensed with. The human being is not an idealized individual -- as believed, say, by libertarians and objectivists -- but nor is he subordinate to a collective blob, as believed by leftists.
Rather, to be a person is "fundamentally to enter upon a relationship with others so as to converge upon a Whole." The chronically rebellious individual is just the other side of the slavishly conformist liberal, because both are equally repelled by real intimacy and communion.
This process of differentiation and union can only occur in time, hence the centrality of history to Christian metaphysics: "since the flow of time is irreversible nothing occurs in it more than once, so that every action takes on a special dignity and an awful gravity; and it is because the world is a history, a single history, that each individual life is a drama" (emphasis mine).
Again, this single drama is the drama of awakening to the cosmic person. Or, in the words of the title of another book we've been discussing, the cosmic movement runs from big bang to big mystery.
Thus, the person is ultimate, but with an important caveat: that there can be no person in the absence of other persons. Personhood is always, and can only be, a result of ex-change with other persons.
Therefore, just as there is a total biosphere, and beneath that a total system of physics and astrocosmology -- there is a single system of personhood. Call it the "psychosphere," or "pneumasphere" if you like. But we like to call it the cOʘnosphere.
At the center, or bottom, or ground, each person is simultaneously centripetal and centrifugal, within which we may "discern the stamp of the creating Trinity," like so:
"There is no solitary person: each one in his very being must give back to all.... It is like a two-way method of exchange, a twofold mode of presence." And "a person is a whole world," except that "this 'world' presupposes others with which it makes up one world only" (ibid).
De Lubac quotes Augustine, who asked, What is more yours than you? Yet what is less yours than you if what you are is from another?
Good question. I'm running out of time, so I'll just get to the upshot of it all, except that I'm going to take the extreme liberty of replacing certain words with empty pneumaticons, so as to not alienate non-Christian readers:
"By revealing O and by being revealed by him, ʘ completes the revelation of man to himself. By taking possession of man, by seizing hold of him and penetrating to the very depths of his being (↓) makes man go deep down within himself, there to discover in a flash regions hitherto unsuspected. It is through (↑) that the person reaches maturity, that man emerges definitively from the universe, and becomes conscious of his own being."