This Psalm finds David at a low point. He is ailing, weary, depressed. We’re given no context for his situation, though it seems he is expecting wrath and discipline, so we can assume he is feeling the need to repent from some sinful action. Exaggeration is common in the psalms to really emphasis the emotion, so it is possible that the physical symptoms David describes are just an example of that, or it could also be that he is feeling sick with guilt, that his sin has caused a physical reaction.
He is calling out for grace and mercy. He appeals to God’s goodness by using the covenant name, LORD, Yahweh. He calls on God’s steadfast love. He is in the depths of despair, and yet is confident of God’s answer. In an effort to rid himself of the enemies who are tormenting him, he sends them away, declaring: “The LORD has heard the sound of my weeping. The LORD has heard my plea; the LORD accepts my prayer.” Even though his situation may not have changed yet, David knows that he has been heard, and he knows that God is just and will respond to his cry.
Sin has consequences in our lives, but repentance restores our relationship with God, because He is merciful and will always forgive us when we ask. He always answers when we call to him. We can come to Him with confidence, even when times are tough, and know that we will be heard. We can trust in His steadfast love and trust Him for justice.