Thomas Aquinas, Compendium of Theology

We should note that the disquiet of the will cannot be wholely overcome unless natural desire is completely satisfied. Elements that are by nature destined for union, naturally desire to be united to each other; for any being seeks what is suited to it by nature. Since, therefore, the natural condition of the human soul is to be united to the body, as was pointed out above, it has a natural desire for union with the body. Hence the will cannot be perfectly at rest until the soul is again joined to the body. When this takes place, man rises from the dead.

Besides, final perfection requires possession of a being's original perfection. But the first perfection of anything requires that it be perfect in its nature, and final perfection consists in attainment of the last end. In order, therefore, that the human soul may be brought to complete perfection with regard to its end, it must be perfect in its nature. This is impossible unless the soul is united to the body. For by nature the soul is a part of man as his form. But no part is perfect in its nature unless it exists in its whole. Therefore man's final happiness requires the soul to be again united to the body.

Moreover, the accidental and all that is contrary to nature cannot be everlasting. But a state wherein the soul is separated from the body is surely per accidens and contrary to nature, if naturally and per se the soul has a longing for union with the body. Therefore the soul will not be forever separated from the body. Accordingly, since the soul's substance is incorruptible, as was shown above, we conclude that the soul is to be reunited to the body.