Charles H. Spurgeon on Psalms 109:6

He begins to prophesy what they should receive for their great impiety, detailing their lot in such a manner as if he wished its realization from a desire of revenge: while he declareth what was to happen with the most absolute certainty, and what of God's justice would worthily come upon such. Some not understanding this mode of predicting the future under the appearance of wishing evil, suppose hatred to be returned for hatred, and an evil will for an evil will: since in truth it belongeth to few to distinguish in what way the punishment of the wicked pleaseth the accuser, who longeth to satiate his enmity; and in how widely different a way it pleaseth the judge, who with a righteous mind punishes sins. For the former returneth evil for evil, but the judge when he punishes does not return evil for evil, since he returneth justice to the unjust; and what is just is surely good. He therefore punishes not from delight in another's misery, which is evil for evil, but from love of justice, which is good for evil. Let not then the blind pervert the light of the Scriptures imagining that God doth not punish sins: nor let the wicked flatter themselves, as if he rendered evil for evil. Let us therefore hear the sequel of this divine composition; and in the words of one who seemeth to wish ill, let us recognise the predictions of a prophet; and let us see God making a just retribution, raising our mind up to his eternal laws. —Augustine.

Verses 6-19. These terrible curses are repeated with many words and sentences, that we may know that David has not let these words fall rashly or from any precipitate impulse of mind; but, the Holy Spirit having dictated, he employs this form of execration that it may be a perpetual prophecy or prediction of the bitter pains and destruction of the enemies of the Church of God. Nor does David imprecate these punishments so much on his own enemies and Judas the betrayer of Christ; but that similar punishments await all who fight against the kingdom of Christ. —Mollerus.

Verses 6-20. I had also this consideration, that if I should now venture all for God, I engaged God to take care of my concerns; but if I forsook him and his ways for fear of any trouble that should come to me or mine, then I should not only falsify my profession, but should count also that my concerns were not so sure, if left at God's feet, while I stood to and for his name, as they would be if they were under my own tuition (or care) though with the denial of the way of God. This was a smarting consideration, and was as spurs unto my flesh. This Scripture (Ps 109:6-20.) also greatly helped it to fasten the more upon me, where Christ prays against Judas, that God would disappoint him in all his selfish thoughts, which moved him to sell his master: pray read it soberly. I had also another consideration, and that was, the dread of the torments of hell, which I was sure they must partake of, that for fear of the cross to shrink from their profession of Christ, his words, and laws, before the sons of men. I thought also of the glory that he had prepared for those that, in faith, and love, and patience, stood to his ways before them. These things, I say, have helped me, when the thoughts of the misery that both myself and mine might for the sake of my profession be exposed to hath lain pinching on my mind. —John Bunyan.