John Gill Commentary Psalms 64:7

"But God will shoot at them; With an arrow suddenly shall they be wounded." — Psalms 64:7 (ASV)

But God shall shoot at them [with] an arrow
With one or other of his four judgments; famine, pestilence, sword, and wild beasts, (Ezekiel 14:21) ; which he brings upon wicked men; and may be compared to arrows, as they are, (Ezekiel 5:16Ezekiel 5:17) (Psalms 91:5Psalms 91:6) (Deuteronomy 32:41Deuteronomy 32:42) ; because they move swiftly. The judgment of wicked men lingereth not, though it may seem to do so; and because they often come suddenly and at an unawares, when men are crying Peace, peace; and because they are sharp and piercing, penetrate deep and stick fast, and wound and kill; they are not arrows of deliverance, unless to the Lord's people, who, by his judgments on the wicked, are delivered from them; but destroying ones, (2 Kings 13:17) (Psalms 144:6) ;

when God draws the bow and shoots, execution is done. This is said in opposition to what wicked men do, (Psalms 64:3Psalms 64:4) ; and in just retaliation; they shoot at the perfect, and God shoots at them;

suddenly shall they be wounded ;
with the wound of an enemy, with the chastisement of a cruel one, with a deadly wound that shall never be healed; not with the arrow of God's word, but with the stroke of his hand; which comes suddenly, falls heavy, and makes the wound incurable.