We should further understand that delight is engendered by the apprehension of a suitable good. Thus sight rejoices in beautiful colors, and taste in sweet savors. But this delight of the senses can be prevented if the organ is indisposed; the same light that is charming to healthy eyes is annoying to sore eyes. However, since the intellect does not understand by employing a bodily organ, as we showed above, no sorrow mars the delight that consists in the contemplation of truth. Of course, sadness can indirectly attend the mind’s contemplation, when the object of truth is apprehended as harmful. Thus knowledge of truth may cause pleasure in ‘the intellect, while at the same time the object known may engender sorrow in the will, not precisely because the object is known, but because its action is pernicious. God, however, by the very fact that He exists, is truth. Therefore the intellect that sees God cannot but rejoice in the vision of Him.
Besides, God is goodness itself, and goodness is the cause of love. Hence God’s goodness must necessarily be loved by all who apprehend it. Although an object that is good may fail to call forth love, or may even be hated, the reason is not that it is apprehended as good, but that it is apprehended as harmful. Consequently in the vision of God, who is goodness and truth itself, there must be love or joyous fruition, no less than comprehension. This accords with Isaiah 66:14: “You shall see and your heart shall rejoice.”
St. Thomas Aquinas. (1265-1274). Compendium Theologiae: Supreme Perfection and Happiness in the Vision of God, trans. by Cyril Vollert. St. Louis & London: B. Herder Book Co., 1947
All scripture is given by inspiration of God and is profitable for doctrine, reproof, correction, and instruction in righteousness (2 Timothy 3:16).