Objection 1. It would seem that the ashes from which the human body will be restored will have a natural inclination towards the soul which will be united to them. For if they had no inclination towards the soul, they would stand in the same relation to that soul as other ashes. Therefore it would make no difference whether the body that is to be united to that soul were restored from those ashes or from others: and this is false.
Objection 2. Further, the body is more dependent on the soul than the soul on the body. Now the soul separated from the body is still somewhat dependent on the body, wherefore its movement towards God is retarded on account of its desire for the body, as Augustine says (Gen. ad lit. xii). Much more, therefore, has the body when separated from the soul, a natural inclination towards that soul.
Objection 3. Further, it is written (Job 20:11): "His bones shall be filled with the vices of his youth, and they shall sleep with him in the dust." But vices are only in the soul. Therefore there will still remain in those ashes a natural inclination towards the soul.
On the contrary, The human body can be dissolved into the very elements, or changed into the flesh of other animals. But the elements are homogeneous, and so is the flesh of a lion or other animal. Since then in the other parts of the elements or animals there is no natural inclination to that soul, neither will there be an inclination towards the soul in those parts into which the human body has been changed. The first proposition is made evident on the authority of Augustine (Enchiridion lxxxviii): "The human body, although changed into the substance of other bodies or even into the elements, although it has become the food and flesh of any animals whatsoever, even of man, will in an instant return to that soul which erstwhile animated it, making it a living and growing man."
Further, to every natural inclination there corresponds a natural agent: else nature would fail in necessaries. Now the aforesaid ashes cannot be reunited to the same soul by any natural agent. Therefore there is not in them any natural inclination to the aforesaid reunion.
I answer that, Opinion is threefold on this point. For some say that the human body is never dissolved into its very elements; and so there always remains in the ashes a certain force besides the elements, which gives a natural inclination to the same soul. But this assertion is in contradiction with the authority of Augustine quoted above, as well as with the senses and reason: since whatever is composed of contraries can be dissolved into its component parts. Wherefore others say that these parts of the elements into which the human body is dissolved retain more light, through having been united to the soul, and for this reason have a natural inclination to human souls. But this again is nonsensical, since the parts of the elements are of the same nature and have an equal share of light and darkness. Hence we must say differently that in those ashes there is no natural inclination to resurrection, but only by the ordering of Divine providence, which decreed that those ashes should be reunited to the soul: it is on this account that those parts of the elements shall be reunited and not others.
Hence the Reply to the First Objection is clear.
Reply to Objection 2. The soul separated from the body remains in the same nature that it has when united to the body. It is not so with the body, and consequently the comparison fails.
Reply to Objection 3. These words of Job do not mean that the vices actually remain in the ashes of the dead, but that they remain according to the ordering of Divine justice, whereby those ashes are destined to the restoration of the body which will suffer eternally for the sins committed.
Source: Summa Theologica (New Advent)