What does Psalm 38:6 mean?

In verse 4, David described suffering under God's convicting rebuke as an enormous burden. Here, he adds details which echo that imagery. The picture set up here is that of a person bent over, flattened to the ground by a heavy load. The body can respond to emotional pain in numerous ways, such as curling forward, lifting the shoulders, or covering the face. As he mourns for his sin, David is wracked and has the posture of a feeble, fallen old man. Further, David indicates that his sense of conviction for his sin (Psalm 38:18) is unending. This is not a momentary feeling, but a perpetual awareness of his guilt. Like a mourner at a funeral, David was filled with sadness; his joy had fled from him.

God does not intend His people to live permanently in experiences such as mourning and sadness. The Lord wants His people to rejoice even amidst trials. Writing to the Philippian church from prison, where he experienced harsh treatment, Paul rejoiced in the Lord and admonished the Philippian believers to rejoice (Philippians 1:3–4, 18; 2:2, 17–18; 3:1; 4:1, 4). Joy and rejoicing don't require happy circumstances—when we follow God's will and still suffer, we can still rejoice in God's provision and protection. Yet if we violate the Lord's will, our suffering is a reason for mourning, followed by repentance and restoration.

This is one reason Jesus urged His followers to keep His commandments (John 15:10). He said, "I have spoken to you, that my joy may be in you, and that your joy may be full" (John 15:11). David's lack of joy was a direct consequence of violating God's will through sin.