11 These passages prove what his view is regarding the resurrection. For he evidently maintains that all bodies will perish and that we shall be incorporeal as according to him we were before we received our present bodies. Again when he comes to argue for a variety of worlds and to maintain that angels will become demons, demons either angels or men, and men in their turn demons; in a word that everything will be turned into something else, he thus sums up his own opinion: “no doubt, after an interval matter will exist afresh and bodies will be formed and a different world will be created to meet the varying wills of reasonable beings who, having forfeited the perfect bliss which continues to the end, have gradually fallen into so great wickedness as to change their nature and refuse to keep their first estate of unalloyed blessedness.
Many reasonable beings, it is right to say, keep it until a second, a third, and a fourth world, and give God no ground for changing their condition. Others deteriorate so little that they seem to have lost hardly anything, and others again have to be hurled headlong into the abyss. God who orders all things alone knows how to use each class according to its deserts in a suitable sphere; for He only understands opportunities and motives and the course in which the world must be steered.
Thus one who has borne away the palm for wickedness and has sunk into the lowest degradation will in the world which is hereafter to be fashioned be made a devil, a kind of first fruits of the Lord's handiwork, to be a laughing stock to the angels who have lost their first virtue.” What is this but to argue that the sinful men of this world may become a devil and demons in another; and contrariwise that those who are now demons may hereafter become either men or angels? And after a lengthy discussion in which he maintains that all corporeal creatures must exchange their material for subtle and spiritual bodies and that all substance must become one pure and inconceivably bright body, of which the human mind can at present form no conception, he winds up thus:— “'God shall be all in all;' that is to say, all bodily existence shall be made as perfect as possible; it shall be brought into the divine essence, than which there is none better.”
Source: Letters (New Advent)