What does Psalm 17:10 mean?

David reports that his enemies (Psalm 17:9) purposely withhold sympathy from their victims. They are heartless and boastful about their criminal activity. Their continual refusal to obey God (Psalm 16:4) while leading a violent lifestyle (Psalm 17:4) had given them callous hearts and seared consciences (1 Timothy 4:2). Proverbs 29:1 offers a stern warning to such hard-hearted people: "He who is often reproved, yet stiffens his neck, will suddenly be broken beyond healing."

The decline into a heartless condition is both gradual and a conscious choice. King Saul started out with humility, but gradually became arrogant and disobeyed the Lord. Ultimately, he resorted to hatred and an insatiable desire to kill David (1 Samuel 20:32–33). Paul predicts in 2 Timothy 3:1–4 that evil men will emerge who are proud, arrogant, unholy, heartless, slanderous, brutal, treacherous, and reckless. He advises Timothy to avoid such people (2 Timothy 3:5). David's enemies and the men Paul describes, demonstrate the truth of Jeremiah 17:9 that the heart is "deceitful above all things, and desperately sick."