Both of the following claims are plausible to me but appear to be in tension:
- A full finite "Aristotelian" life of seriously attempting to practice the intellectual and ethical virtues could be satisfactory.
- I rightly find a finite purely natural life unsatisfactory (our hearts are rightly restless until they find rest in God).
But now observe that (1) and (2) are not logically contradictory. To see that, notice that there are several logically possible stories to be told on which both (1) and (2) are true. The first story is that of grace and fallenness: I am fallen, and without the supernatural component of grace in my life, I couldn't actually lead a life of seriously attempting to practice the virtues—I would, instead, slide into vice unless I happened to die early (in which case the life wouldn't be "full"), and eventually I would abandon the serious attempts to practice the virtues. If that story is true, then (2) is true, because any finite purely natural life would be a life without grace (by definition of "natural") and hence could not be a full "Aristotelian" life.
A second, complementary way to reconcile (1) and (2) is this. I have received the grace of longing for the joy of supernatural union with God. The grace of Christ both makes me long for that joy and directs me to it. As a result of that grace, my heart is restless unless it rests in God. (I don't know if Augustine would allow that the truth of his dictum is dependent on grace.) Given the grace to have the intensively infinite beatitude of union with God, any purely natural life would indeed be objectively unsatisfactory. But, nonetheless, an Aristotelian life could be fully satisfactory—not to me as I am, but to a hypothetical human being who is both unfallen (and hence can live the Aristotelian life) and has not received the grace of that longing.
A generalization of the second way to reconcile (1) and (2) is this. We read (1) in this way: There are possible beings in many ways like us who would be rightly satisfied by a finite Aristotelian life. But these possible beings are not us. Here, "are not us" can be read in two ways. First, as we did in the second way: they are not us who are graced with a longing for God. Second, we could have a completely different reading: they are not human. On this reading, the finite Aristotelian life is not a life for human beings, but for perhaps hypothetical non-humans who do not have the infinite beatitude of union with God as their telos. This gives us a third way to reconcile (1) and (2).
However, a natural human life is indeed sufficient to fulfill the human being's natural needs. It takes grace to long for more than the natural needs. So human beings should, in fact, be able to be satisfied with a natural life, absent grace, at least if they are unfallen. This makes the third way to reconcile (1) and (2) problematic. However we can focus not on the naturalness of the Aristotelian life in (1), but on its finitude. It may be that living forever is actually natural to us. (That we needed the fruit of the tree of life is compatible with this, because there is nothing absurd about needing external goods to live out our nature.) If so, then the beings that would rightly be satisfied with a finite Aristotelian life (note that Aristotle himself was open to the possibility of an afterlife) are not humans.
These three answers appear compatible with one another, and all appear plausible, so the full story is that an infinite Aristotelian life would be satisfactory to us, if we were unfallen and ungraced, but fallen as we all are, and by and large graced as we are (I think grace is offered to all at some point, but for some that point may not yet have come), we rightly find the thought of such a life insufficient. And a finite Aristotelian life would be satisfactory only to humanoids who are not human. The story also explains why some people might find an infinite Aristotelian life satisfactory—for they have not received grace—and why some might feel satisfied by the thought of a finite Aristotelian life—for their aspirations are lowered by the fall.