The essence of happiness consists in an act of the intellect. (Thomas Aquinas, Summa Theologica) … What is implicit in this sentence? This is implicit: the fulfillment of existence takes place in the manner in which we become aware of reality; the whole energy of our being is ultimately directed toward attainment of insight. The perfectly happy person, the one whose thirst has been finally quenched, who has attained beatitude—this person is the one who sees. The happiness, the quenching, the perfection, consists in this seeing.

p. 58 - Happiness and Contemplation (1958)