Objection 1. It would seem that man's happiness consists in bodily goods. For it is written (Sirach 30:16): "There is no riches above the riches of the health of the body." But happiness consists in that which is best. Therefore it consists in the health of the body.
Objection 2. Further, Dionysius says (Div. Nom. v), that "to be" is better than "to live," and "to live" is better than all that follows. But for man's being and living, the health of the body is necessary. Since, therefore, happiness is man's supreme good, it seems that health of the body belongs more than anything else to happiness.
Objection 3. Further, the more universal a thing is, the higher the principle from which it depends; because the higher a cause is, the greater the scope of its power. Now just as the causality of the efficient cause consists in its flowing into something, so the causality of the end consists in its drawing the appetite. Therefore, just as the First Cause is that which flows into all things, so the last end is that which attracts the desire of all. But being itself is that which is most desired by all. Therefore man's happiness consists most of all in things pertaining to his being, such as the health of the body.
On the contrary, Man surpasses all other animals in regard to happiness. But in bodily goods he is surpassed by many animals; for instance, by the elephant in longevity, by the lion in strength, by the stag in fleetness. Therefore man's happiness does not consist in goods of the body.
I answer that, It is impossible for man's happiness to consist in the goods of the body; and this for two reasons. First, because, if a thing be ordained to another as to its end, its last end cannot consist in the preservation of its being. Hence a captain does not intend as a last end, the preservation of the ship entrusted to him, since a ship is ordained to something else as its end, viz. to navigation. Now just as the ship is entrusted to the captain that he may steer its course, so man is given over to his will and reason; according to Sirach 15:14: "God made man from the beginning and left him in the hand of his own counsel." Now it is evident that man is ordained to something as his end: since man is not the supreme good. Therefore the last end of man's reason and will cannot be the preservation of man's being.
Secondly, because, granted that the end of man's will and reason be the preservation of man's being, it could not be said that the end of man is some good of the body. For man's being consists in soul and body; and though the being of the body depends on the soul, yet the being of the human soul depends not on the body, as shown above (I, 75, 2); and the very body is for the soul, as matter for its form, and the instruments for the man that puts them into motion, that by their means he may do his work. Wherefore all goods of the body are ordained to the goods of the soul, as to their end. Consequently happiness, which is man's last end, cannot consist in goods of the body.
Reply to Objection 1. Just as the body is ordained to the soul, as its end, so are external goods ordained to the body itself. And therefore it is with reason that the good of the body is preferred to external goods, which are signified by "riches," just as the good of the soul is preferred to all bodily goods.
Reply to Objection 2. Being taken simply, as including all perfection of being, surpasses life and all that follows it; for thus being itself includes all these. And in this sense Dionysius speaks. But if we consider being itself as participated in this or that thing, which does not possess the whole perfection of being, but has imperfect being, such as the being of any creature; then it is evident that being itself together with an additional perfection is more excellent. Hence in the same passage Dionysius says that things that live are better than things that exist, and intelligent better than living things.
Reply to Objection 3. Since the end corresponds to the beginning; this argument proves that the last end is the first beginning of being, in Whom every perfection of being is: Whose likeness, according to their proportion, some desire as to being only, some as to living being, some as to being which is living, intelligent and happy. And this belongs to few.
Source: Summa Theologica (New Advent)