Say not so, she replied; to talk so also is blasphemous. Rather, as the Scripture tells you, say that the one is like the other. For that which is “made in the image” of the Deity necessarily possesses a likeness to its prototype in every respect; it resembles it in being intellectual, immaterial, unconnected with any notion of weight, and in eluding any measurement of its dimensions; yet as regards its own peculiar nature it is something different from that other. Indeed, it would be no longer an “image,” if it were altogether identical with that other; but where we have A in that uncreate prototype we have a in the image; just as in a minute particle of glass, when it happens to face the light, the complete disc of the sun is often to be seen, not represented thereon in proportion to its proper size, but so far as the minuteness of the particle admits of its being represented at all. Thus do the reflections of those ineffable qualities of Deity shine forth within the narrow limits of our nature; and so our reason, following the leading of these reflections, will not miss grasping the Mind in its essence by clearing away from the question all corporeal qualities; nor on the other hand will it bring the pure and infinite Existence to the level of that which is perishable and little; it will regard this essence of the Mind as an object of thought only, since it is the “image” of an Existence which is such; but it will not pronounce this image to be identical with the prototype. Just, then, as we have no doubts, owing to the display of a Divine mysterious wisdom in the universe, about a Divine Being and a Divine Power existing in it all which secures its continuance (though if you required a definition of that Being you would therein find the Deity completely sundered from every object in creation, whether of sense or thought, while in these last, too, natural distinctions are admitted), so, too, there is nothing strange in the soul's separate existence as a substance (whatever we may think that substance to be) being no hindrance to her actual existence, in spite of the elemental atoms of the world not harmonizing with her in the definition of her being. In the case of our living bodies, composed as they are from the blending of these atoms, there is no sort of communion, as has been just said, on the score of substance, between the simplicity and invisibility of the soul, and the grossness of those bodies; but, notwithstanding that, there is not a doubt that there is in them the soul's vivifying influence exerted by a law which it is beyond the human understanding to comprehend. Not even then, when those atoms have again been dissolved into themselves, has that bond of a vivifying influence vanished; but as, while the framework of the body still holds together, each individual part is possessed of a soul which penetrates equally every component member, and one could not call that soul hard and resistent though blended with the solid, nor humid, or cold, or the reverse, though it transmits life to all and each of such parts, so, when that framework is dissolved, and has returned to its kindred elements, there is nothing against probability that that simple and incomposite essence which has once for all by some inexplicable law grown with the growth of the bodily framework should continually remain beside the atoms with which it has been blended, and should in no way be sundered from a union once formed. For it does not follow that because the composite is dissolved the incomposite must be dissolved with it.
That those atoms, I rejoined, should unite and again be separated, and that this constitutes the formation and dissolution of the body, no one would deny. But we have to consider this. There are great intervals between these atoms; they differ from each other, both in position, and also in qualitative distinctions and peculiarities. When, indeed, these atoms have all converged upon the given subject, it is reasonable that that intelligent and undimensional essence which we call the soul should cohere with that which is so united; but once these atoms are separated from each other, and have gone whither their nature impels them, what is to become of the soul when her vessel is thus scattered in many directions? As a sailor, when his ship has been wrecked and gone to pieces, cannot float upon all the pieces at once which have been scattered this way and that over the surface of the sea (for he seizes any bit that comes to hand, and lets all the rest drift away), in the same way the soul, being by nature incapable of dissolution along with the atoms, will, if she finds it hard to be parted from the body altogether, cling to some one of them; and if we take this view, consistency will no more allow us to regard her as immortal for living in one atom than as mortal for not living in a number of them.
But the intelligent and undimensional, she replied, is neither contracted nor diffused (contraction and diffusion being a property of body only); but by virtue of a nature which is formless and bodiless it is present with the body equally in the contraction and in the diffusion of its atoms, and is no more narrowed by the compression which attends the uniting of the atoms than it is abandoned by them when they wander off to their kindred, however wide the interval is held to be which we observe between alien atoms. For instance, there is a great difference between the buoyant and light as contrasted with the heavy and solid; between the hot as contrasted with the cold; between the humid as contrasted with its opposite; nevertheless it is no strain to an intelligent essence to be present in each of those elements to which it has once cohered; this blending with opposites does not split it up. In locality, in peculiar qualities, these elemental atoms are held to be far removed from each other; but an undimensional nature finds it no labour to cling to what is locally divided, seeing that even now it is possible for the mind at once to contemplate the heavens above us and to extend its busy scrutiny beyond the horizon, nor is its contemplative power at all distracted by these excursions into distances so great. There is nothing, then, to hinder the soul's presence in the body's atoms, whether fused in union or decomposed in dissolution. Just as in the amalgam of gold and silver a certain methodical force is to be observed which has fused the metals, and if the one be afterwards smelted out of the other, the law of this method nevertheless continues to reside in each, so that while the amalgam is separated this method does not suffer division along with it (for you cannot make fractions out of the indivisible), in the same way this intelligent essence of the soul is observable in the concourse of the atoms, and does not undergo division when they are dissolved; but it remains with them, and even in their separation it is co-extensive with them, yet not itself dissevered nor discounted into sections to accord with the number of the atoms. Such a condition belongs to the material and spacial world, but that which is intelligent and undimensional is not liable to the circumstances of space. Therefore the soul exists in the actual atoms which she has once animated, and there is no force to tear her away from her cohesion with them. What cause for melancholy, then, is there herein, that the visible is exchanged for the invisible; and wherefore is it that your mind has conceived such a hatred of death?
Source: On the Soul and the Resurrection (New Advent)