In Psalm 64, last in the group of four psalms here, David prays for protection from those plotting against him and meditates on the sudden judgment that awaits the wicked.

The rebels "encourage themselves" by scheming and coming up with the "perfect plan" (compare verses 5-6). By saying that the inward thought and heart of man are "deep" (verse 6), David seems to be saying that they are hidden deep down where no one would see, following the question in verse 5. But Someone does see. The Nelson Study Bible states: "The arrogance of the wicked in their plots against the righteous is a continuing theme in the Psalms (Psalm 9; 10; 12). Who will see [they think to themselves]: The wicked do not know, or do not care, that there is One who sees (Psalm 73:11), and who will repay (Psalm 75:7)" (note on Psalm 64:5-6). Jeremiah quoted God as saying: "The heart is deceitful above all things, and desperately wicked; who can know it? I, the Lord, search the heart, I test the mind, even to give every man according to his ways, according to the fruit of his doings" (Jeremiah 17:9-10).

Indeed, David believes that God will punish the wicked based on the principle of just retribution. Their "arrows" or "bitter words" (verses 3-4) God will shoot back at them (verse 7). "He will make them stumble over their own tongue" (verse 8) is not a reference to stuttering but that their own words will ultimately trip them up and bring them down. In essence, what they plan to do to others will "come back to bite them" and bring about their own downfall (compare Galatians 6:7).

This will be a lesson to all (Psalm 64:9). In addition to fearing God, they will "declare the work of God," passing on to others what they have witnessed, and "wisely consider" what He has done (same verse). In light of God's faithfulness, David in verse 10 encourages the godly to trust and rely on Him.