Have mercy upon me, O LORD; for I am weak: O LORD, heal me; for my bones are vexed.
Bones — My inmost parts.
 For in death there is no remembrance of thee: in the grave who shall give thee thanks?
In death — Among the dead.
Remembrance — He speaks of the remembrance or celebration of God's grace in the land of the living, to the edification of God's church, and the propagation of true religion among men; which is not done in the other life.
 I am weary with my groaning; all the night make I my bed to swim; I water my couch with my tears.
With my tears — It well becomes the greatest spirits to be tender, and to relent under the tokens of God's displeasure. David who could face Goliath himself, melts into tears at the remembrance of sin, and under the apprehension of Divine wrath, and it is no diminution to his character.
 Depart from me, all ye workers of iniquity; for the LORD hath heard the voice of my weeping.
Hath heard — By the workings of God's grace upon his heart, he knew his prayer was accepted. His tears had a voice, in the ears of the God of mercy. Silent tears are no speechless ones. Our tears are cries to God.
 Let all mine enemies be ashamed and sore vexed: let them return and be ashamed suddenly.
Ashamed — Of their vain confidence.
Return — Repent of their sins and return to their obedience.