Have mercy upon me, O LORD; for I am weak: O LORD, heal me; for my bones are vexed.
For I am weak - `faint' х 'umlal (H536), from 'aamal (H535), to droop as a plant]. David's plea is not that his sufferings are not deserved, but that his pain is in bringing him to that extremity from which God's fatherly mercy cannot but deliver His child. The believer is the object of God's love, even in thy sufferings, which God's anger at sin inflicts. When, then, he has been brought to the verge of his powers of endurance (1 Corinthians 10:13), God, who designs by sufferings to consume in him the remainders of sin, and not to destroy him as He does the ungodly, turns, and has mercy on him, in answer to his believing cry.
Heal me - both, in body and spirit.
My bones are vexed - literally, 'terrified,' nibhalu, my acute distress paralyzes all my limbs.