Objection 1. It would seem that the bodies of the damned will be impassible. For, according to the Philosopher (Topic. vi), "increase of passion results in loss of substance." Now "if a finite thing be continually lessened, it must needs at length be done away" (Phys. i, 4). Therefore if the bodies of the damned will be passible, and will be ever suffering, they will at length be done away and corrupted: and this has been shown to be false (2). Therefore they will be impassible.
Objection 2. Further, every agent likens the patient to itself. If then the bodies of the damned are passive to the fire the fire will liken them to itself. Now fire does not consume bodies except in so far as in likening them to itself it disintegrates them. Therefore if the bodies of the damned will be passible they will at length be consumed by the fire, and thus the same conclusion follows as before.
Objection 3. Further, those animals, for instance the salamander, which are said to remain living in fire without being destroyed, are not distressed by the fire: because an animal is not distressed by bodily pain, unless the body in some way is hurt thereby. If therefore the bodies of the damned can, like the aforesaid animals, remain in the fire without being corrupted, as Augustine asserts (De Civ. Dei xxi, 2,4), it would seem that they will suffer no distress there: which would not be the case unless their bodies were impassible. Therefore, etc.
Objection 4. Further, if the bodies of the damned be passible, the pain resulting from their suffering, seemingly, will surpass all present bodily pain, even as the joy of the saints will surpass all present joy. Now in this life it sometimes happens that the soul is severed from the body through excess of pain. Much more therefore if those bodies will be passible, the souls will be separate from the bodies through excess of pain, and thus those bodies will be corrupted: which is false. Therefore those bodies will be impassible.
On the contrary, It is written (1 Corinthians 15:52): "And we shall be changed": and a gloss says: "We--the good alone--will be changed with the unchangeableness and impassibility of glory."
Further, even as the body co-operates with the soul in merit, so does it co-operate in sin. Now on account of the former co-operation not only the soul but also the body will be rewarded after the resurrection. Therefore in like manner the bodies of the damned will be punished; which would not be the case were they impassible. Therefore they will be passible.
I answer that, The principal cause of the bodies of the damned not being consumed by fire will be the Divine justice by which their bodies will be consigned to everlasting punishment. Now the Divine justice is served also by the natural disposition, whether on the part of the passive body or on the part of the active causes; for since passiveness is a kind of receptiveness, there are two kinds of passion, corresponding to two ways in which one thing is receptive of another. For a form may be received into a subject materially according to its natural being, just as the air receives heat from fire materially; and corresponding to this manner of reception there is a kind of passion which we call "passion of nature." In another way one thing is received into another spiritually by way of an "intention," just as the likeness of whiteness is received into the air and in the pupil: this reception is like that whereby the soul receives the likeness of things: wherefore corresponding to this mode of reception is another mode of passion which we call "passion of the soul." Since therefore after the resurrection and the cessation of the heavenly movement it will be impossible for a body to be altered by its natural quality, as stated above (Article 2), it will not be possible for any body to be passive with a passion of nature. Consequently as regards this mode of passion the bodies of the damned will be impassible even as they will be incorruptible. Yet after the heaven has ceased to move, there will still remain the passion which is after the manner of the soul, since the air will both receive light from the sun, and will convey the variety of colors to the sight. Wherefore in respect of this mode of passion the bodies of the damned will be passible. But the glorified bodies, albeit they receive something, and are in a manner patient to sensation, will nevertheless not be passive, since they will receive nothing to distress or hurt them, as will the bodies of the damned, which for this reason are said to be passible.
Reply to Objection 1. The Philosopher is speaking of the passion whereby the patient is changed from its natural disposition. But this kind of passion will not be in the bodies of the damned, as stated above.
Reply to Objection 2. The likeness of the agent is in the patient in two ways. First, in the same way as in the agent, and thus it is in all univocal agents, for instance a thing that is hot makes another thing hot, and fire generates fire. Secondly, otherwise than in the agent, and thus it is in all equivocal agents. In these it happens sometimes that a form which is in the agent spiritually is received into the patient materially: thus the form of the house built by the craftsman is materially in itself, but spiritually in the mind of the craftsman. On the other hand, sometimes it is in the agent materially, but is received into the patient spiritually: thus whiteness is materially on the wall wherein it is received, whereas it is spiritually in the pupil and in the transferring medium. And so it is in the case at issue, because the species which is in the fire materially is received spiritually into the bodies of the damned; thus it is that the fire will assimilate the bodies of the damned to itself, without consuming them withal.
Reply to Objection 3. According to the Philosopher (De Prop. Element.), "no animal can live in fire." Galen also (De simp. medic.) says "that there is no body which at length is not consumed by fire"; although sometimes certain bodies may remain in fire without hurt, such as ebony. The instance of the salamander is not altogether apposite, since it cannot remain in the fire without being at last consumed, as do the bodies of the damned in hell. Nor does it follow that because the bodies of the damned suffer no corruption from the fire, they therefore are not tormented by the fire, because the sensible object has a natural aptitude to please or displease the senses, not only as regards its natural action of stimulating or injuring the organ, but also as regards its spiritual action: since when the sensible object is duly proportionate to the sense, it pleases, whereas the contrary is the result when it is in excess or defect. Hence subdued colors and harmonious sounds are pleasing, whereas discordant sounds displease the hearing.
Reply to Objection 4. Pain does not sever the soul from the body, in so far as it is confined to a power of the soul which feels the pain, but in so far as the passion of the soul leads to the body being changed from its natural disposition. Thus it is that we see that through anger the body becomes heated, and through fear, chilled: whereas after the resurrection it will be impossible for the body to be changed from its natural disposition, as stated above (Article 2). Consequently, however great the pain will be, it will not sever the body from the soul.
Source: Summa Theologica (New Advent)