What does Psalm 40:13 mean?

David cries out to God not only to save him, but to do so quickly. This has a dual meaning: David acknowledged his need for forgiveness of sins (Psalm 40:12), as well as the physical dangers he often faced (Psalm 3:1–2; 17:8–9). David was keenly aware of how much he needed the Lord. For all his success, he knew he could not overcome either sin or worldly enemies through his own strength.

Samson, a judge of Israel, should have humbly submitted to the fact that the Lord was the source of his strength. Yet, when the Philistines were ready to capture him, he depended on his past record of victories for victory. He was mistaken. He boasted: "I will go out as at other times and shake myself free" (Judges 16:20). However, Samson's pride and sin had caused God to withdraw His protective power. Arrogance leads to defeat, whereas confidence in the Lord leads to victory. Proverbs 16:18 warns, "Pride goes before destruction, and a haughty spirit before a fall." No wonder the apostle Paul exhorted Timothy to draw his strength from the grace that is in the Lord (2 Timothy 2:1).