Objection 1. It would seem that in happiness, delight ranks before vision. For "delight is the perfection of operation" (Ethic. x, 4). But perfection ranks before the thing perfected. Therefore delight ranks before the operation of the intellect, i.e. vision.
Objection 2. Further, that by reason of which a thing is desirable, is yet more desirable. But operations are desired on account of the delight they afford: hence, too, nature has adjusted delight to those operations which are necessary for the preservation of the individual and of the species, lest animals should disregard such operations. Therefore, in happiness, delight ranks before the operation of the intellect, which is vision.
Objection 3. Further, vision corresponds to faith; while delight or enjoyment corresponds to charity. But charity ranks before faith, as the Apostle says (1 Corinthians 13:13). Therefore delight or enjoyment ranks before vision.
On the contrary, The cause is greater than its effect. But vision is the cause of delight. Therefore vision ranks before delight.
I answer that, The Philosopher discusses this question (Ethic. x, 4), and leaves it unsolved. But if one consider the matter carefully, the operation of the intellect which is vision, must needs rank before delight. For delight consists in a certain repose of the will. Now that the will finds rest in anything, can only be on account of the goodness of that thing in which it reposes. If therefore the will reposes in an operation, the will's repose is caused by the goodness of the operation. Nor does the will seek good for the sake of repose; for thus the very act of the will would be the end, which has been disproved above (1, 1, ad 2; 3, 4): but it seeks to be at rest in the operation, because that operation is its good. Consequently it is evident that the operation in which the will reposes ranks before the resting of the will therein.
Reply to Objection 1. As the Philosopher says (Ethic. x, 4) "delight perfects operation as vigor perfects youth," because it is a result of youth. Consequently delight is a perfection attendant upon vision; but not a perfection whereby vision is made perfect in its own species.
Reply to Objection 2. The apprehension of the senses does not attain to the universal good, but to some particular good which is delightful. And consequently, according to the sensitive appetite which is in animals, operations are sought for the sake of delight. But the intellect apprehends the universal good, the attainment of which results in delight: wherefore its purpose is directed to good rather than to delight. Hence it is that the Divine intellect, which is the Author of nature, adjusted delights to operations on account of the operations. And we should form our estimate of things not simply according to the order of the sensitive appetite, but rather according to the order of the intellectual appetite.
Reply to Objection 3. Charity does not seem the beloved good for the sake of delight: it is for charity a consequence that it delights in the good gained which it loves. Thus delight does not answer to charity as its end, but vision does, whereby the end is first made present to charity.
Source: Summa Theologica (New Advent)