Albert Barnes Commentary Psalms 58:8

"[Let them be] as a snail which melteth and passeth away, [Like] the untimely birth of a woman, that hath not seen the sun." — Psalms 58:8 (ASV)

As a snail which melteth, let every one of them pass away - Or rather, as the snail which melts as it goes; that is, which leaves a slimy trail as it moves along, and thus melts away the more as it advances, until eventually it dies. Gesenius, Lexicon. The allusion is to what seems to occur to the snail; it seems to melt or to be dissolved as it moves along; or seems to leave a part of itself in the slime which flows from it.

Like the untimely birth of a woman - The Hebrew word literally means “that which falls from a woman;” and therefore, the word is used to denote an abortion. The prayer is that they might utterly pass away, that they might become like those who never had real life, and that their power might wholly disappear.

That they may not see the sun - May not be among the living. Compare the notes at Job 3:16.