Let all mine enemies be ashamed - Be so brought to see their folly that they shall be ashamed of their conduct. The wish is that they might be brought to see their own guilt - a wish certainly which it is right to cherish in regard to all evil-doers.
And sore vexed - Compare the notes at Psalm 5:10. The same Hebrew word is used here which occurs in Psalm 6:2-3, and rendered "vexed." It is a word which denotes trouble, trembling, consternation; and the meaning here is, that the psalmist prayed that they might be confounded or disconcerted in their plans - a prayer which is certainly proper in regard to all the purposes of the wicked. No one should desire that the purposes of the wicked should prosper; and not to desire this is to desire that they may be foiled and overcome in their schemes. This must be the wish of every good man.
Let them return - Turn back, or be turned back; that is, let them be repulsed, and compelled to turn back from their present object.
And be ashamed suddenly - Hebrew, "In a moment;" instantaneously. He desired that there might be no delay, but that their defeat might be accomplished at once. As it was right to pray that this might occur, so it was right to pray that it might occur without delay, or as speedily as possible. The sooner the plans of sinners are confounded, the better.

Ashamed and sore vexed - May they as deeply deplore their transgressions as I have done mine! May they return; may they be suddenly converted! The original will bear this meaning, and it is the most congenial to Christian principles.

Let all mine enemies be ashamed and sore vexed: let them return [and] be ashamed (f) suddenly.
(f) When the wicked think the godly will perish, God delivers them suddenly, and destroys their enemies.

Let all mine enemies be ashamed,.... Or "they shall be ashamed" (k); and so the following clauses may be rendered, and be considered as prophecies of what would be; though if this be considered as an imprecation, it is wishing no ill; wicked men are not ashamed of their abominations committed by them, neither can they blush; it would be well if they were ashamed of them, and brought to true repentance for them; and if they are not ashamed now, they will be hereafter, when the Judge of quick and dead appears;
and sore vexed; or "troubled" (l); as his bones had been vexed, and his soul had been sore vexed by them; as he knew they would be through disappointment at his recovery, and at his deliverance from the distresses and calamities he was now in, when he should sing for joy of heart, and they should howl for vexation of spirit;
let them return; meaning either from him, from pursuing after him; or to him, to seek his favour, and be reconciled to him, and be at peace with him, as Aben Ezra and Kimchi explain it; unless this word should only signify "again", as it sometimes does, and be read in connection with what follows;
and let them be again ashamed suddenly (m); intimating that his deliverance would be sudden, in a moment, in a very little time, and so would be their disappointment, shame, and confusion. Jarchi, from R. Jonathan and R. Samuel bar Nachmani, refers this to the shame of the wicked in the world to come.
(k) "pudore afficientur", Pagninus, Montanus; "pudefient", Coeceius, Schmidt; so Ainsworth. (l) "conturbantur", Junius & Tremellius, Piscator. (m) "iterum confundantur", Gejerus.

and knows they will be disappointed and in their turn (compare Psalm 6:3) be terror-stricken or confounded.

Ashamed - Of their vain confidence. Return - Repent of their sins and return to their obedience.