In his Eschatology, Ratzinger several times quotes approvingly the claim that matter cannot be perfected. For Aristotle and the Greeks, the claim was not only wrong but confusingly wrong – how could anyone ever say something so obviously stupid? For them, things were material because they are ontological precursors to some other, more complete state. This meaning remains for us as well: call something building materials because we need to do something to make them complete; or course materials because they need to be worked over, written on, assimilated into consciousness, etc. Good grief, not only is material existence completable, completing it is the only reason you call it material.
But the quotation makes perfect sense if matter is viewed not as an ontological precursor but as an eternal, foundational substance. There was a way in which things were material like this for the Greeks too – the heavenly bodies were eternal, fundamental substances that one could not make anything else out of, and so they could never be viewed as stuff that could be worked on to make some later, complete substance. One way to understand modern accounts of matter in ancient categories is to see all reality as being the fundamental particles, which were as eternal, substantial, and unchageable as the the heavenly bodies, while all other things (men, trees, and planets, etc) are no more substantial than the constellations, and for exactly the same reason.
This bivalence is implicit in the nature of matter itself. Matter remains through change and so is both the precursor to some later state and a reality that underlies any of the entities that arise from it and so has a bona fide eternity and foundational character.