Objection 1. It would seem that perfection of the body is not necessary for man's perfect Happiness. For perfection of the body is a bodily good. But it has been shown above (Article 2) that Happiness does not consist in bodily goods. Therefore no perfect disposition of the body is necessary for man's Happiness.
Objection 2. Further, man's Happiness consists in the vision of the Divine Essence, as shown above (Question 3, Article 8). But the body has not part in this operation, as shown above (Article 5). Therefore no disposition of the body is necessary for Happiness.
Objection 3. Further, the more the intellect is abstracted from the body, the more perfectly it understands. But Happiness consists in the most perfect operation of the intellect. Therefore the soul should be abstracted from the body in every way. Therefore, in no way is a disposition of the body necessary for Happiness.
On the contrary, Happiness is the reward of virtue; wherefore it is written (John 13:17): "You shall be blessed, if you do them." But the reward promised to the saints is not only that they shall see and enjoy God, but also that their bodies shall be well-disposed; for it is written (Isaiah 66:14): "You shall see and your heart shall rejoice, and your bones shall flourish like a herb." Therefore good disposition of the body is necessary for Happiness.
I answer that, If we speak of that happiness which man can acquire in this life, it is evident that a well-disposed body is of necessity required for it. For this happiness consists, according to the Philosopher (Ethic. i, 13) in "an operation according to perfect virtue"; and it is clear that man can be hindered, by indisposition of the body, from every operation of virtue.
But speaking of perfect Happiness, some have maintained that no disposition of body is necessary for Happiness; indeed, that it is necessary for the soul to be entirely separated from the body. Hence Augustine (De Civ. Dei xxii, 26) quotes the words of Porphyry who said that "for the soul to be happy, it must be severed from everything corporeal." But this is unreasonable. For since it is natural to the soul to be united to the body; it is not possible for the perfection of the soul to exclude its natural perfection.
Consequently, we must say that perfect disposition of the body is necessary, both antecedently and consequently, for that Happiness which is in all ways perfect. Antecedently, because, as Augustine says (Gen. ad lit. xii, 35), "if body be such, that the governance thereof is difficult and burdensome, like unto flesh which is corruptible and weighs upon the soul, the mind is turned away from that vision of the highest heaven." Whence he concludes that, "when this body will no longer be 'natural,' but 'spiritual,' then will it be equalled to the angels, and that will be its glory, which erstwhile was its burden." Consequently, because from the Happiness of the soul there will be an overflow on to the body, so that this too will obtain its perfection. Hence Augustine says (Ep. ad Dioscor.) that "God gave the soul such a powerful nature that from its exceeding fulness of happiness the vigor of incorruption overflows into the lower nature."
Reply to Objection 1. Happiness does not consist in bodily good as its object: but bodily good can add a certain charm and perfection to Happiness.
Reply to Objection 2. Although the body has not part in that operation of the intellect whereby the Essence of God is seen, yet it might prove a hindrance thereto. Consequently, perfection of the body is necessary, lest it hinder the mind from being lifted up.
Reply to Objection 3. The perfect operation of the intellect requires indeed that the intellect be abstracted from this corruptible body which weighs upon the soul; but not from the spiritual body, which will be wholly subject to the spirit. On this point we shall treat in the Third Part of this work (II-II, 82, seqq.).
Source: Summa Theologica (New Advent)