Blessed is the man unto whom the LORD imputeth not iniquity, and in whose spirit there is no guile.
Blessed ... imputeth not iniquity. Compare on the phrase 'impute (i:e., set down to the transgressor's account his) iniquity,' 2 Samuel 19:19. Paul (Romans 4:1-8) quotes this passage as proving the doctrine of man's justification before God by faith, and not by works: to him that believeth, his faith is imputed for righteousness, and the Lord imputes not his iniquity to him for the sake of the merits and blood-shedding of the atoning Saviour, in whom he puts his faith (2 Corinthians 5:19).
And ... guile. The "guile" meant is shown by the contrast, "I acknowledged my sin," "mine iniquity have I not hid." It consists in hiding one's sin, and keeping silence (Psalms 32:3) as to it before God, through pride, love of sin and self, and want of faith toward God. Guile denies, or else extenuates, and seeks apologies for one's sin, and so is incompatible with the bestowal of pardon, and the consequent blessedness of experienced forgiveness. Such was the case with Saul, whose case contrasts with David's, as to the sin, the penitence, and the result respectively, (1 Samuel 13:9-14; 1 Samuel 15:9-30; 2 Samuel 11:1; 2 Samuel 11:12.)