What does Psalm chapter 140 mean?

This is the last of the "imprecatory" psalms (Psalms 5; 10; 17; 35; 58; 59; 69; 70; 79; 83; 109; 129; 137) which call on the Lord to directly punish enemies. David may have written this in response to King Saul's murderous jealousy (1 Samuel 19:1–2). It may also refer to the rebellion of Absalom, David's own son (2 Samuel 15:13–14). The general content is similar to Psalm 7, also written by David in reference to hostile enemies.

First comes David's prayer for rescue. The enemy is depicted as aggressive and wicked. Their violence comes through slander and lies which create conflict. These men also conspire, setting traps and preparing to catch David off-guard. These may be literal or political traps; in either case the aggressors are evil (Psalm 140:1–5).

Next is another statement of the same request. This time, David focuses on his prior experiences with the Lord. Since God has protected David in the past (1 Samuel 17:34–37; 19:10; 2 Samuel 8:14), David has confidence that rescue will come this time, as well. He is entirely loyal to God and doesn't want to see evil people succeed through their schemes (Psalm 140:6–8).

Other Old Testament passages speak about an evil person's own sins coming back to harm them (Psalm 7:14–16; Proverbs 6:32; 26:27; 28:10). Here, David asks that his enemies experience defeat and even death. The reference to the "head" might imply that David is thinking of a specific person who is leading these attacks. Once again, he echoes his concern that evil does not gain a foothold through success. However, these are framed as requests, not vows. David makes no plans to seek revenge (Romans 12:19; Hebrews 10:30); he expresses a desire that God would judge these enemies harshly (Psalm 140:9–11).

Again, David reinforces his faith in God. Based on prior experience, David knows that the Lord is good. He can be trusted in any circumstance. Those who properly honor Him—the "righteous" and "upright"—can expect to be with Him (Psalm 140:12–13).