He shall reward evil unto mine enemies As the verb ysyv, yashib, may be rendered he shall cause to return, [1] it seems to point not only at the punishment, but the kind of punishment, which would be awarded to his enemies, in the recoiling of their wicked machinations upon their own heads. Some give an optative signification to the verb, understanding the words to express a wish or prayer; but I see no reason why it should not be taken strictly in the future tense, and imagine that David intimates his certain expectation that this favor, which he had already prayed for, would be granted. It is by no means uncommon to find the prayers of the Psalmist intersected with sentences of this kind, inserted for the purpose of stimulating his faith, as here, where he announces the general truth, that God is the righteous judge who will recompense the wicked. With the view of confirming his hopes, he adverts particularly to the truth of God; for nothing can support us in the hour of temptation, when the Divine deliverance may be long delayed, but a firm persuasion that God is true, and that he cannot deceive us by his divine promises. His confidence of obtaining his request was grounded upon the circumstance that God could no more deny his word than deny himself.

Footnotes

1 - French and Skinner read, "May their mischief return upon those who watch me;" and observe, "that their mischief in Hebrew is the evil, and that the meaning is, the very evil which they devised against me. Compare Psalm 7:16."

He shall reward evil unto mine enemies - Margin, "those that observe me." The original word here means literally "to twist, to twist together;" then, to press together; then, to "oppress," or to treat as an enemy. The reference here is to those who pressed upon him as enemies, or who endeavored to crush him. The idea is that God would recompense them for this conduct, or that he would deal with them as they deserved.
Cut them off in thy truth - In thy faithfulness; in thy regard for what is right. This is simply a prayer, or an expression of strong confidence, that God would deal with them as they deserved, or that he would not suffer such conduct to pass without a proper expression of his sense of the wrong. There is no evidence that David in this prayer was prompted by private or vindictive feeling.

He shall reward evil - Saul and his courtiers, instead of having God's approbation, shall have his curse.
Cut them off in thy truth - Thou hast promised to save me; these have purposed to destroy me. Thy truth is engaged in my defence; they will destroy me if permitted to live: to save thy truth, and to accomplish its promises, thou must cut them off.

He shall reward evil unto mine enemies: cut them off in thy (e) truth.
(e) According to your faithful promise for my defence.

He shall reward evil unto mine enemies,.... That eyed him as Saul did; that observed his haunts, where he resorted, and who were with him, as the Ziphites did under Saul's direction; as the Word (m) here used for "enemies" signifies: the mischief they had devised for him, he believed, would be returned upon their own heads; the pit they digged they would fall into themselves; and the net they had spread for others their own feet would be taken in. This was true as of David's enemies, so of Christ's, the wicked Jews, who narrowly watched him to take every advantage against him;
cut them off in thy truth; root and branch, as Saul, and his family, and his courtiers, quickly were, according to the truth of promises made to David, and of threatenings unto them.
(m) "observatoribus meis", Junius & Tremellius, Piscator, Michaelis.

He shall . . . evil--or, "Evil shall return on" (Psalm 7:16) my enemies or watchers, that is, to do me evil (Psalm 6:7).
in thy truth--Thy verified promise.

Thy truth - Whereby thou art engaged to fulfil thy promises and threatenings.