Matthew Poole and continuators on Psalms 28:4

4. Give them according to their deeds, and according to the wickedness of their endeavours : give them after the work of their hands, render to them their desert.

David useth these Imprecations partly to Vindicate himself from the slanders of his Enemies, who Reported him to be as wicked as they were, only more close and Cunning therein; which if he had been, he had bitterly Cursed himself; which it could not reasonably be presumed that he would do: Partly, from his great and long Experience of their implacable and incorrigible Malignity, not only against him, but against God, and his declared Will, and against all truly good Men, and that covered with Pretences of Piety to God, and of Peaceableness towards their Neighbours, v. 3. which made their wickedness more inexcusable and detestable: Partly by the instinct and direction of God's Spirit, by whose inspiration he uttered this, as well as the rest of the Psalm, and Partly, that hereby he might provoke them to Repentance; for this Curse belongs only to those, who shall Obstinately persist in their wicked Courses. Add to all this, that as Verbs of the Imperative Mood, are oft used by the Hebrews for Futures, so these may not be proper Imprecations, but predictions of their Destruction.