Objection 1. It would seem that the happiness of the saints will not be greater after the judgment than before. For the nearer a thing approaches to the Divine likeness, the more perfectly does it participate happiness. Now the soul is more like God when separated from the body than when united to it. Therefore its happiness is greater before being reunited to the body than after.
Objection 2. Further, power is more effective when it is united than when divided. Now the soul is more united when separated from the body than when it is joined to the body. Therefore it has then greater power for operation, and consequently has a more perfect share of happiness, since this consists in action [Cf. I-II, 3, 2].
Objection 3. Further, beatitude consists in an act of the speculative intellect. Now the intellect, in its act, makes no use of a bodily organ; and consequently by being reunited to the body the soul does not become capable of more perfect understanding. Therefore the soul's happiness is not greater after than before the judgment.
Objection 4. Further, nothing can be greater than the infinite, and so the addition of the finite to the infinite does not result in something greater than the infinite by itself. Now the beatified soul before its reunion with the body is rendered happy by rejoicing in the infinite good, namely God; and after the resurrection of the body it will rejoice in nothing else except perhaps the glory of the body, and this is a finite good. Therefore their joy after the resumption of the body will not be greater than before.
On the contrary, A gloss on Apocalypse 6:9, "I saw under the altar the souls of them that were slain," says: "At present the souls of the saints are under the altar, i.e. less exalted than they will be." Therefore their happiness will be greater after the resurrection than after their death.
Further, just as happiness is bestowed on the good as a reward, so is unhappiness awarded to the wicked. But the unhappiness of the wicked after reunion with their bodies will be greater than before, since they will be punished not only in the soul but also in the body. Therefore the happiness of the saints will be greater after the resurrection of the body than before.
I answer that, It is manifest that the happiness of the saints will increase in extent after the resurrection, because their happiness will then be not only in the soul but also in the body. Moreover, the soul's happiness also will increase in extent, seeing that the soul will rejoice not only in its own good, but also in that of the body. We may also say that the soul's happiness will increase in intensity [Cf. I-II, 4, 5, ad 5, where St. Thomas retracts this statement]. For man's body may be considered in two ways: first, as being dependent on the soul for its completion; secondly, as containing something that hampers the soul in its operations, through the soul not perfectly completing the body. As regards the first way of considering the body, its union with the soul adds a certain perfection to the soul, since every part is imperfect, and is completed in its whole; wherefore the whole is to the part as form to matter. Consequently the soul is more perfect in its natural being, when it is in the whole--namely, man who results from the union of soul and body--than when it is a separate part. But as regards the second consideration the union of the body hampers the perfection of the soul, wherefore it is written (Wisdom 9:15) that "the corruptible body is a load upon the soul." If, then, there be removed from the body all those things wherein it hampers the soul's action, the soul will be simply more perfect while existing in such a body than when separated therefrom. Now the more perfect a thing is in being, the more perfectly is it able to operate: wherefore the operation of the soul united to such a body will be more perfect than the operation of the separated soul. But the glorified body will be a body of this description, being altogether subject to the spirit. Therefore, since beatitude consists in an operation [Cf. I-II, 3, 2, seqq.], the soul's happiness after its reunion with the body will be more perfect than before. For just as the soul separated from a corruptible body is able to operate more perfectly than when united thereto, so after it has been united to a glorified body, its operation will be more perfect than while it was separated. Now every imperfect thing desires its perfection. Hence the separated soul naturally desires reunion with the body and on account of this desire which proceeds from the soul's imperfection its operation whereby it is borne towards God is less intense. This agrees with the saying of Augustine (Gen. ad lit. xii, 35) that "on account of the body's desire it is held back from tending with all its might to that sovereign good."
Reply to Objection 1. The soul united to a glorified body is more like to God than when separated therefrom, in so far as when united it has more perfect being. For the more perfect a thing is the more it is like to God: even so the heart, the perfection of whose life consists in movement, is more like to God while in movement than while at rest, although God is never moved.
Reply to Objection 2. A power which by its own nature is capable of being in matter is more effective when subjected in matter than when separated from matter, although absolutely speaking a power separate from matter is more effective.
Reply to Objection 3. Although in the act of understanding the soul does not make use of the body, the perfection of the body will somewhat conduce to the perfection of the intellectual operation in so far as through being united to a glorified body, the soul will be more perfect in its nature, and consequently more effective in its operation, and accordingly the good itself of the body will conduce instrumentally, as it were, to the operation wherein happiness consists: thus the Philosopher asserts (Ethic. i, 8,10) that external goods conduce instrumentally to the happiness of life.
Reply to Objection 4. Although finite added to infinite does not make a greater thing, it makes more things, since finite and infinite are two things, while infinite taken by itself is one. Now the greater extent of joy regards not a greater thing but more things. Wherefore joy is increased in extent, through referring to God and to the body's glory, in comparison with the joy which referred to God. Moreover, the body's glory will conduce to the intensity of the joy that refers to God, in so far as it will conduce to the more perfect operation whereby the soul tends to God: since the more perfect is a becoming operation, the greater the delight [Cf. I-II, 32, 1], as stated in Ethic. x, 8.
Source: Summa Theologica (New Advent)