My tears have been my meat - The word rendered tears in this place is in the singular number, and means literally weeping. Compare Psalms 39:12. The word meat here means literally bread, and is used in the general signification of food, as the word meat is always used in the English version of the Bible. The English word meat, which originally signified food, has been changed gradually in its signification, until it now denotes in common usage animal food, or flesh. The idea here is, that instead of eating, he had wept. The state described is that which occurs so often when excessive sorrow takes away the appetite, or destroys the relish for food, and occasions fasting. This was the foundation of the whole idea of fasting - that sorrow, and especially sorrow for sin, takes away the desire for food for the time, and leads to involuntary abstinence. Hence arose the correlative idea of abstaining from food with a view to promote that deep sense of sin, or to produce a condition of the body which would be favorable to a proper recollection of guilt.
Day and night - Constantly; without intermission. See the notes at Psalms 1:2. “While they continually say unto me.” While it is constantly said to me; that is, by mine enemies. See Psalms 42:10.
Where is thy God? - See Psalms 3:2; Psalms 22:8. The meaning here is, “He seems to be utterly forsaken or abandoned by God. He trusted in God. He professed to be his friend. He looked to him as his protector. But he is now forsaken, as if he had no God; and God is treating him as if he were none of his; as if he had no love for him, and no concern about his welfare.”