According to the schoolmen, the reason why any substance is changeable is because its matter is not fully actuated by its substantial form, and thus remains in potentiality to other forms. The heavenly spheres (corpora coelestia) they thought were fully actuated by their forms, and were therefore imperishable. They applied this doctrine to the body after the resurrection, saying that then the body, whether of a good or of a wicked man, was fully actuated by the soul, and therefore was incorruptible. This doctrine however had its difficulties, as we see here, in respect of the lost being subject to sensible pain, and even the just being susceptible of pleasurable impressions of sense. Cf. II, Chap. XCVIII (a passage not translated): "The matter of a heavenly sphere is so thoroughly perfected by its own form as not to lie potentially open to other forms." Just so is every risen human body, good or bad.

Of God and His Creatures: 4.89