What does Psalm 31:10 mean?

The reference to "iniquity" here is obscure. At least some of David's troubles are blamed on this flaw. He does not identify any specific sin. Still, the presence of that sin led to spiritual weakness, and that led to physical weakness (Psalm 31:9). To his credit, David was aware of his sin and its consequences. He openly asked for God's gracious lenience. David's plea here might be a way of confessing his sin while noting its devastating effects.

In Old Testament thought, bones were the essence of a person's physical form. The same Hebrew term, 'etsem, means both "bones" and "self" or "essence." Speaking of someone's bones referred to deep, critical issues (Psalm 38:3; 102:3). Bones are typically the longest-lasting part of a body (Genesis 50:25; Exodus 13:19). When bones are decomposing or weakening, it's a sign of terrible distress.

It's possible this psalm was written around the same time as Psalm 32. In that song, David notes that when he kept silent about his sin of adultery, he was wracked by weakness and misery (Psalm 32:3–4). He recognized that God was convicting him of his sin and his strength vanished. However, when he confessed his sin, the Lord forgave him (Psalm 32:5). Believers should not try to cover up their sins. Proverbs 28:13 warns: "Whoever conceals his transgressions will not prosper." However, the same verse promises: "But he who confesses and forsakes them will obtain mercy."