John Calvin Commentary Psalms 109:24

"My knees are weak through fasting; And my flesh faileth of fatness." — Psalms 109:24 (ASV)

My knees have become feeble. Though David had the necessities of life, he still emaciated himself by voluntary abstinence, to which, as well as to prayer, he devoted himself. Therefore, we may regard this verse as expressive of his sorrow and sadness. We may also understand it as expressive of his having no relish for food or drink, since we know that people who are in sorrow and sadness have no appetite for food; even life itself is burdensome to them.

If anyone prefers restricting the interpretation to David’s being in want of the necessities of life—when he hid himself in the dens of wild beasts to escape the fury of his enemies and was then subjected to hunger and thirst—he may do so. It appears to me, however, that by this language David intends to point out the extreme anguish he felt. Because, with death staring him in the face, he loathed all food. This is in accordance with the next clause, in which he says, my flesh fails of fatness; because a sorrowful spirit dries up the bones (Proverbs 17:22).

By the term “fatness,” some understand delicacies, meaning that he was deprived of all food that is pleasing to the palate. The more natural way is to consider it as denoting his becoming emaciated by reason of grief and fasting, since the natural moisture was wasted.

Another proof of his sad situation arises from this: according to what he states in Psalm 22:7, he was held in scorn by all. It is, indeed, a sad and bitter thing that God’s children endure when they are made to feel that the curse He pronounces against the transgressors of His law is directed against themselves. For the law says to its despisers, You shall become an astonishment, a proverb, and a laughingstock (Deuteronomy 28:37).

David was assailed with this kind of temptation. He declares that he was not only regarded as a condemned person but also cruelly derided, and God, at the same time, was also subjected to a share of it. For it is typical for the ungodly to conduct themselves with insolence and pride towards us when they see us oppressed by afflictions. At the same time, they rail at our faith and piety because God offers us no help in our miseries.