Chapter 151 — How the rational soul must be reunited with the body for perfect beatitude

We should note that there cannot be unchangeability of will in every way unless natural desire is completely satisfied. Things 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 human soul is naturally united to the body, as was shown 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—which is for man to rise from the dead.

Besides, a being’s final perfection requires its first perfection. But the first perfection of anything is that it be perfect in its nature, while its final perfection consists in attainment of its last end. In order, therefore, that the human soul may be brought to perfection in every way in its end, it must be perfect in its nature. This is impossible unless the soul is united to the body. For the soul’s nature is to be a part of man as his form. But no part is perfect in its nature unless it is in its whole. Therefore, man’s final happiness requires the soul to be again united to the body.

Moreover, the incidental and all that is contrary to nature cannot be everlasting. But a state wherein the soul is separated from the body must be incidental and contrary to nature, if it is in the soul naturally and of itself that the soul be united with the body. Therefore, the soul will not be separated from the body forever. Accordingly, since the soul’s substance is incorruptible, as was shown above, we conclude that the soul is to be reunited to the body.