What does Psalm 139:19 mean?

Scripture does not shy away from the cries of human hearts, even when those desires seem dark or troubled. Here, David longs for God to kill the wicked. He knows that in His justice God will dispense judgment on those who violate His laws. David describes the wicked as "men of blood," and he wanted nothing to do with them. It's noteworthy that David does not declare his intent to kill evil people on God's behalf, or ask God to appoint him to that task. He states his desire, but leaves the matter in God's hands.

Job, too, wanted God to slay the wicked. He wondered why they lived long and prospered (Job 21:7, 13), and prayed, "Let their own eyes see their destruction, and let them drink of the wrath of the Almighty" (Job 21:20). Like Job, we may wonder why God doesn't punish the wicked immediately. One reason is that God hates sin but patiently waits for sinners to repent (2 Peter 3:9). He will execute justice in due time, but until then He extends His invitation to accept His mercy and pardon (Isaiah 55:6–7).

The apostle Paul was once a blasphemer and a murderer, but God's love, mercy, and grace reached him and turned Christianity's chief antagonist into its chief advocate (Galatians 1:13–16; 1 Timothy 1:12–16).