Miracles do not overturn the natural limits of the dead
Augustine is answering the objection that martyrs must know what the living do, since they appear and grant benefits to those who pray.
This also solves the question of how martyrs show that they are involved in human affairs through the very favors granted to those who pray, if the dead do not know what the living are doing. For we have heard—not from uncertain rumors but from reliable witnesses—that the confessor Felix, whose dwelling you devoutly love, appeared not only through the effects of his favors but even to people's very sight when Nola was being attacked by barbarians. But such things are shown forth by God in a way far different from the usual order assigned to each kind of creature. For water was suddenly turned into wine when the Lord willed it, but that does not mean we should fail to recognize what water can do in its own proper order among the elements, apart from the rarity or rather the uniqueness of that divine work. Nor does the fact that Lazarus rose mean that every dead person rises whenever he wishes, or that a lifeless body is roused by a living person the way a sleeper is roused by someone awake. Human affairs have their limits; signs of divine powers are something else. Some things happen naturally, others miraculously—though God is present to nature, that it may be, and nature is not absent from miracles. So we should not think that any dead person can be involved in the affairs of the living just because martyrs are present to heal or help certain people. Rather, we should understand that martyrs are involved in the affairs of the living through divine power, precisely because the dead by their own nature cannot be involved in the affairs of the living.
Latin
Hinc et illa soluitur quaestio, quomodo martyres ipsis beneficiis, quae dantur orantibus, indicant se interesse rebus humanis, si nesciunt mortui, quid agant uiui. non enim solis beneficiorum effectibus, uerum ipsis etiam hominum aspectibus confessorem adparuisse Felicem, cuius inquilinatum pie diligis, cum a barbaris Nola obpugnaretur, audiuimus non incertis rumoribus, sed testibus certis. uerum ista diuinitus exhibentur longe aliter, quam sese habet usitatus ordo singulis creaturarum generibus adtributus. non enim quia in uinum aqua, cum uoluit dominus, repente conuersa est, ideo non debemus, quid aqua ualeat in elementorum ordine proprio, ab istius diuini operis raritate uel potius singularitate discernere; nec quoniam Lazarus resurrexit, ideo mortuus omnis, quando uult, surgit aut eo modo exanimis a uiuente quomodo a uigilante dormiens excitatur. alii sunt humanarum limites rerum, alia diuinarum signa uirtutum; alia sunt, quae naturaliter, alia, quae mirabiliter fiunt, quamuis et naturae deus adsit, ut sit, et miraculis natura non desit. non igitur ideo putandum est uiuorum rebus quoslibet interesse posse defunctos, quoniam quibusdam sanandis uel adiuuandis martyres adsunt, sed ideo potius intellegendum est, quod per diuinam potentiam martyres uiuorum rebus intersunt, quoniam defuncti per naturam propriam uiuorum rebus interesse non possunt.