Let them {p} curse, but bless thou: when they arise, let them be ashamed; but let thy servant rejoice.

(p) They will gain nothing by cursing me.

Jamieson-Fausset-Brown Bible Commentary

28-31. In confidence that God's blessing would come on him, and confusion and shame on his enemies (Ps 73:13), he ceases to regard their curses, and anticipates a season of joyful and public thanksgiving; for God is near to protect (Ps 16:8; 34:6) the poor from all unrighteous judges who may condemn him.

Matthew Henry's Concise Commentary

109:21-31 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.