Charles H. Spurgeon on Psalms 28:4

Give them according to their deeds, etc. Here, again, occurs the difficult question about praying for vengeance, which, however, I shall despatch in a few words. In the first place, then, it is unquestionable, that if the flesh move us to seek revenge, the desire is wicked in the sight of God. He not only forbids us to imprecate evil upon our enemies in revenge for private injuries, but it cannot be otherwise than that all those desires which spring from hatred must be disordered. David's example, therefore, must not be alleged by those who are driven by their own intemperate passion to seek vengeance. The holy prophet is not inflamed here by his own private sorrow to devote his enemies to destruction; but laying aside the desire of the flesh, he give judgment concerning the matter itself. Before a man can, therefore, denounce vengeance against the wicked, he must first shake himself free from all improper feelings in his own mind. In the second place, prudence must be exercised, that the heinousness of the evils which offend us drive us not to intemperate zeal, which happened even to Christ's disciples, when they desired that fire might be brought from heaven to consume those who refused to entertain their Master. Lu 9:54. They pretended, it is true, to act according to the example of Elias, but Christ severely rebuked them, and told them that they knew not by what spirit they were actuated. In particular, we must observe this general rule, that we cordially desire and labour for the welfare of the whole human race. Thus it will come to pass, that we shall not only give way to the exercise of God's mercy, but shall also wish the conversion of those who seem obstinately to rush upon their own destruction. In short, David, being free from every evil passion, and likewise endued with the spirit of discretion and judgment, pleads here not so much his own cause as the cause of God. And by this prayer, he further reminds both himself and the faithful, that although the wicked may give themselves loose reins in the commission of every species of vice with impunity for a time, they must at length stand before the judgment seat of God. John Calvin.