Objection 1. It would seem that delight is not required for happiness. For Augustine says (De Trin. i, 8) that "vision is the entire reward of faith." But the prize or reward of virtue is happiness, as the Philosopher clearly states (Ethic. i, 9). Therefore nothing besides vision is required for happiness.
Objection 2. Further, happiness is "the most self-sufficient of all goods," as the Philosopher declares (Ethic. i, 7). But that which needs something else is not self-sufficient. Since then the essence of happiness consists in seeing God, as stated above (Question 3, Article 8); it seems that delight is not necessary for happiness.
Objection 3. Further, the "operation of bliss or happiness should be unhindered" (Ethic. vii, 13). But delight hinders the operation of the intellect: since it destroys the estimate of prudence (Ethic. vi, 5). Therefore delight is not necessary for happiness.
On the contrary, Augustine says (Confess. x, 23) that happiness is "joy in truth."
I answer that, One thing may be necessary for another in four ways. First, as a preamble and preparation to it: thus instruction is necessary for science. Secondly, as perfecting it: thus the soul is necessary for the life of the body. Thirdly, as helping it from without: thus friends are necessary for some undertaking. Fourthly, as something attendant on it: thus we might say that heat is necessary for fire. And in this way delight is necessary for happiness. For it is caused by the appetite being at rest in the good attained. Wherefore, since happiness is nothing else but the attainment of the Sovereign Good, it cannot be without concomitant delight.
Reply to Objection 1. From the very fact that a reward is given to anyone, the will of him who deserves it is at rest, and in this consists delight. Consequently, delight is included in the very notion of reward.
Reply to Objection 2. The very sight of God causes delight. Consequently, he who sees God cannot need delight.
Reply to Objection 3. Delight that is attendant upon the operation of the intellect does not hinder it, rather does it perfect it, as stated in Ethic. x, 4: since what we do with delight, we do with greater care and perseverance. On the other hand, delight which is extraneous to the operation is a hindrance thereto: sometimes by distracting the attention because, as already observed, we are more attentive to those things that delight us; and when we are very attentive to one thing, we must needs be less attentive to another: sometimes on account of opposition; thus a sensual delight that is contrary to reason, hinders the estimate of prudence more than it hinders the estimate of the speculative intellect.
Source: Summa Theologica (New Advent)