15 “Since they have embittered You, O Lord: I am,” says He, “the Bread which came down from heaven;” again, “Labour for the meat which wasts not;” again, “Taste and see that the Lord is sweet.” But to sinners the bread of truth is bitter. Whence they hate the mouth of him that speaks the truth. These then have embittered God, who by sin have fallen into such a state of sickliness, that the food of truth, in which healthy souls delight, as if it were bitter as gall, they cannot bear.
Source: The Enarrations, or Expositions, on the Psalms (New Advent)