Have mercy upon me, O Lord - That is, be gracious to me; or, show me compassion. This language may be used either in view of sin, of suffering, or of danger. It is a cry to God to interpose, and remove some present source of trouble, and may be employed by one who feels that he is a sinner, or by one on a bed of pain, or by one surrounded by enemies, or by one at the point of death, or by one who is looking out with apprehension upon the eternal world. It is commonly, indeed (compare Psalms 51:1), a cry to God in view of sin, pleading for pardon and salvation; but here it is a cry in view of trouble and danger, outward sorrow and mental anguish, that had overcome the strength of the sufferer and laid him on a bed of languishing. See introduction to the psalm, Section 3.
For I am weak - The original word here, אמלל 'ûmlal, means properly to languish or droop, as plants do that are blighted, Isaiah 24:7, or as fields do in a drought, Isaiah 16:8, and is here applied to a sick person whose strength is withered and gone. The condition of such an one is beautifully compared with a plant that withers for lack of moisture; and the word is used in this sense here, as referring to the psalmist himself when sick, as the result of his outward and mental sorrows. Such an effect has not been uncommon in the world. There have been numberless cases where sorrow has prostrated the strength - as a plant withers - and has brought on languishing sickness.
O Lord, heal me - This is language which would be properly applied to a case of sickness, and therefore, it is most natural to interpret it in this sense in this place. Compare Isaiah 19:22; Isaiah 30:26; Job 5:18; Genesis 20:17; Psalms 60:2; 2 Chronicles 16:12; Deuteronomy 28:27.
For my bones are vexed - The word “vexed” we now commonly apply to mental trouble, and especially the lighter sort of mental trouble - to irritate, to make angry by little provocations, to harass. It is used here, however, as is common in the Scriptures, in reference to torment or to anguish. The bones are the strength and framework of the body, and the psalmist means here to say that the very source of his strength was gone; that that which supported him was prostrated; that his disease and sorrow had penetrated the most firm parts of his body. Language is often used in the Scriptures, also, as if the “bones” actually suffered pain, though it is now known that the bones, as such, are incapable of pain. And in the same manner, also, language is often used, though that use of the word is not found in the Scriptures, as if the “marrow” of the bones were especially sensitive, like a nerve, in accordance with what is the common and popular belief, though it is now known that the marrow of the bones is entirely insensible to suffering. The design of the psalmist here is to say that he was crushed and afflicted in every part of his frame.