Complete Commentary on the Whole Bible, by Matthew Henry, at sacred-texts.com
(Psa 140:1-7) David encourages himself in God.
(Psa 140:8-13) He prays for, and prophesies the destruction of, his persecutors.
The more danger appears, the more earnest we should be in prayer to God. All are safe whom the Lord protects. If he be for us, who can be against us? We should especially watch and pray, that the Lord would hold up our goings in his ways, that our footsteps slip not. God is as able to keep his people from secret fraud as from open force; and the experience we have had of his power and care, in dangers of one kind, may encourage us to depend upon him in other dangers.
Believers may pray that God would not grant the desires of the wicked, nor further their evil devices. False accusers will bring mischief upon themselves, even the burning coals of Divine vengeance. And surely the righteous shall dwell in God's presence, and give him thanks for evermore. This is true thanksgiving, even thanks-living: this use we should make of all our deliverances, we should serve God the more closely and cheerfully. Those who, though evil spoken of and ill-used by men, are righteous in the sight of God, being justified by the righteousness of Christ, which is imputed to them, and received by faith, as the effect of which, they live soberly and righteously; these give thanks to the Lord, for the righteousness whereby they are made righteous, and for every blessing of grace, and mercy of life.