Psalms 54:5

5.He shall reward evil unto mine enemies As the verb ישיב , yashib, may be rendered he shall cause to return, (292) 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.