Complete Commentary on the Whole Bible, by Matthew Henry, at sacred-texts.com
(Psa 109:1-5) David complains of his enemies.
(Psa 109:6-20) He prophesies their destruction.
(Psa 109:21-31) Prayers and praises.
It is the unspeakable comfort of all believers, that whoever is against them, God is for them; and to him they may apply as to one pleased to concern himself for them. David's enemies laughed at him for his devotion, but they could not laugh him out of it.
The Lord Jesus may speak here as a Judge, denouncing sentence on some of his enemies, to warn others. When men reject the salvation of Christ, even their prayers are numbered among their sins. See what hurries some to shameful deaths, and brings the families and estates of others to ruin; makes them and theirs despicable and hateful, and brings poverty, shame, and misery upon their posterity: it is sin, that mischievous, destructive thing. And what will be the effect of the sentence, "Go, ye cursed," upon the bodies and souls of the wicked! How it will affect the senses of the body, and the powers of the soul, with pain, anguish, horror, and despair! Think on these things, sinners, tremble and repent.
The psalmist takes God's comforts to himself, but in a very humble manner. He was troubled in mind. His body was wasted, and almost worn away. But it is better to have leanness in the body, while the soul prospers and is in health, than to have leanness in the soul, while the body is feasted. He was ridiculed and reproached by his enemies. But if God bless us, we need not care who curses us; for how can they curse whom God has not cursed; nay, whom he has blessed? He pleads God's glory, and the honour of his name. Save me, not according to my merit, for I pretend to none, but according to thy-mercy. He concludes with the joy of faith, in assurance that his present conflicts would end in triumphs. Let all that suffer according to the will of God, commit the keeping of their souls to him. Jesus, unjustly put to death, and now risen again, is an Advocate and Intercessor for his people, ever ready to appear on their behalf against a corrupt world, and the great accuser.