Why, seeing that Lazarus' soul is occupied with his present blessings and turns round to look at nothing that he has left, while the rich man is still attached, with a cement as it were, even after death, to the life of feeling, which he does not divest himself of even when he has ceased to live, still keeping as he does flesh and blood in his thoughts (for in his entreaty that his kindred may be exempted from his sufferings he plainly shows that he is not freed yet from fleshly feeling)—in such details of the story (she continued) I think our Lord teaches us this; that those still living in the flesh must as much as ever they can separate and free themselves in a way from its attachments by virtuous conduct, in order that after death they may not need a second death to cleanse them from the remnants that are owing to this cement of the flesh, and, when once the bonds are loosed from around the soul, her soaring up to the Good may be swift and unimpeded, with no anguish of the body to distract her. For if any one becomes wholly and thoroughly carnal in thought, such an one, with every motion and energy of the soul absorbed in fleshly desires, is not parted from such attachments, even in the disembodied state; just as those who have lingered long in noisome places do not part with the unpleasantness contracted by that lengthened stay, even when they pass into a sweet atmosphere. So it is that, when the change is made into the impalpable Unseen, not even then will it be possible for the lovers of the flesh to avoid dragging away with them under any circumstances some fleshly foulness; and thereby their torment will be intensified, their soul having been materialized by such surroundings. I think too that this view of the matter harmonizes to a certain extent with the assertion made by some persons that around their graves shadowy phantoms of the departed are often seen. If this is really so, an inordinate attachment of that particular soul to the life in the flesh is proved to have existed, causing it to be unwilling, even when expelled from the flesh, to fly clean away and to admit the complete change of its form into the impalpable; it remains near the frame even after the dissolution of the frame, and though now outside it, hovers regretfully over the place where its material is and continues to haunt it.
Then, after a moment's reflection on the meaning of these latter words, I said: I think that a contradiction now arises between what you have said and the result of our former examination of the passions. For if, on the one hand, the activity of such movements within us is to be held as arising from our kinship with the brutes, such movements I mean as were enumerated in our previous discussion, anger, for instance, and fear, desire of pleasure, and so on, and, on the other hand, it was affirmed that virtue consists in the good employment of these movements, and vice in their bad employment, and in addition to this we discussed the actual contribution of each of the other passions to a virtuous life, and found that through desire above all we are brought nearer God, drawn up, by its chain as it were, from earth towards Him—I think (I said) that that part of the discussion is in a way opposed to that which we are now aiming at.
How so? She asked.
Why, when every unreasoning instinct is quenched within us after our purgation, this principle of desire will not exist any more than the other principles; and this being removed, it looks as if the striving after the better way would also cease, no other emotion remaining in the soul that can stir us up to the appetence of Good.
Source: On the Soul and the Resurrection (New Advent)