I do not think, she replied, that the divine Apostle divided the intellectual world into localities, when he named part as in heaven, part as on earth, and part as under the earth. There are three states in which reasoning creatures can be: one from the very first received an immaterial life, and we call it the angelic: another is in union with the flesh, and we call it the human: a third is released by death from fleshly entanglements, and is to be found in souls pure and simple. Now I think that the divine Apostle in his deep wisdom looked to this, when he revealed the future concord of all these reasoning beings in the work of goodness; and that he puts the unembodied angel-world “in heaven,” and that still involved with a body “on earth,” and that released from a body “under the earth”; or, indeed, if there is any other world to be classed under that which is possessed of reason (it is not left out); and whether any one choose to call this last “demons” or “spirits,” or anything else of the kind, we shall not care. We certainly believe, both because of the prevailing opinion, and still more of Scripture teaching, that there exists another world of beings besides, divested of such bodies as ours are, who are opposed to that which is good and are capable of hurting the lives of men, having by an act of will lapsed from the nobler view, and by this revolt from goodness personified in themselves the contrary principle; and this world is what, some say, the Apostle adds to the number of the “things under the earth,” signifying in that passage that when evil shall have been some day annihilated in the long revolutions of the ages, nothing shall be left outside the world of goodness, but that even from those evil spirits shall rise in harmony the confession of Christ's Lordship. If this is so, then no one can compel us to see any spot of the underworld in the expression, “things under the earth”; the atmosphere spreads equally over every part of the earth, and there is not a single corner of it left unrobed by this circumambient air.
When she had finished, I hesitated a moment, and then said: I am not yet satisfied about the thing which we have been inquiring into; after all that has been said my mind is still in doubt; and I beg that our discussion may be allowed to revert to the same line of reasoning as before, omitting only that upon which we are thoroughly agreed. I say this, for I think that all but the most stubborn controversialists will have been sufficiently convinced by our debate not to consign the soul after the body's dissolution to annihilation and nonentity, nor to argue that because it differs substantially from the atoms it is impossible for it to exist anywhere in the universe; for, however much a being that is intellectual and immaterial may fail to coincide with these atoms, it is in no ways hindered (so far) from existing in them; and this belief of ours rests on two facts: firstly, on the soul's existing in our bodies in this present life, though fundamentally different from them: and secondly, on the fact that the Divine being, as our argument has shown, though distinctly something other than visible and material substances, nevertheless pervades each one among all existences, and by this penetration of the whole keeps the world in a state of being; so that following these analogies we need not think that the soul, either, is out of existence, when she passes from the world of forms to the Unseen. But how, I insisted, after the united whole of the atoms has assumed, owing to their mixing together, a form quite different— the form in fact with which the soul has been actually domesticated— by what mark, when this form, as we should have expected, is effaced along with the resolution of the atoms, shall the soul follow along (them), now that that familiar form ceases to persist?
She waited a moment and then said: Give me leave to invent a fanciful simile in order to illustrate the matter before us: even though that which I suppose may be outside the range of possibility. Grant it possible, then, in the art of painting not only to mix opposite colours, as painters are always doing, to represent a particular tint, but also to separate again this mixture and to restore to each of the colours its natural dye. If then white, or black, or red, or golden colour, or any other colour that has been mixed to form the given tint, were to be again separated from that union with another and remain by itself, we suppose that our artist will none the less remember the actual nature of that colour, and that in no case will he show forgetfulness, either of the red, for instance, or the black, if after having become quite a different colour by composition with each other they each return to their natural dye. We suppose, I say, that our artist remembers the manner of the mutual blending of these colours, and so knows what sort of colour was mixed with a given colour and what sort of colour was the result, and how, the other colour being ejected from the composition, (the original colour) in consequence of such release resumed its own peculiar hue; and, supposing it were required to produce the same result again by composition, the process will be all the easier from having been already practised in his previous work. Now, if reason can see any analogy in this simile, we must search the matter in hand by its light. Let the soul stand for this Art of the painter; and let the natural atoms stand for the colours of his art; and let the mixture of that tint compounded of the various dyes, and the return of these to their native state (which we have been allowed to assume), represent respectively the concourse, and the separation of the atoms. Then, as we assume in the simile that the painter's Art tells him the actual dye of each colour, when it has returned after mixing to its proper hue, so that he has an exact knowledge of the red, and of the black, and of any other colour that went to form the required tint by a specific way of uniting with another kind— a knowledge which includes its appearance both in the mixture, and now when it is in its natural state, and in the future again, supposing all the colours were mixed over again in like fashion— so, we assert, does the soul know the natural peculiarities of those atoms whose concourse makes the frame of the body in which it has itself grown, even after the scattering of those atoms. However far from each other their natural propensity and their inherent forces of repulsion urge them, and debar each from mingling with its opposite, none the less will the soul be near each by its power of recognition, and will persistently cling to the familiar atoms, until their concourse after this division again takes place in the same way, for that fresh formation of the dissolved body which will properly be, and be called, resurrection.
You seem, I interrupted, in this passing remark to have made an excellent defence of the faith in the Resurrection. By it, I think, the opponents of this doctrine might be gradually led to consider it not as a thing absolutely impossible that the atoms should again coalesce and form the same man as before.
That is very true, the Teacher replied. For we may hear these opponents urging the following difficulty. “The atoms are resolved, like to like, into the universe; by what device, then, does the warmth, for instance, residing in such and such a man, after joining the universal warmth, again dissociate itself from this connection with its kindred, so as to form this man who is being 'remoulded'? For if the identical individual particle does not return and only something that is homogeneous but not identical is fetched, you will have something else in the place of that first thing, and such a process will cease to be a resurrection and will be merely the creation of a new man. But if the same man is to return into himself, he must be the same entirely, and regain his original formation in every single atom of his elements.”
Source: On the Soul and the Resurrection (New Advent)