Verse 19
The waters wear the stones - Even the common stones are affected in the same way. Were even earthquakes and violent concussions of nature wanting, the action of water, either running over them as a stream, or even falling upon them in drops, will wear these stones. Hence the proverb: -
Gutta cavat lapidem non vi sed saepe cadendo. "Constant droppings will make a hole in a flint." Εκ θαμινης ραθαμιγγος, ὁκως λογος, αιες ιοισας, Χ' ἁ λιθος ες ρωχμον κοιλαινεται. "From frequent dropping, as the proverb says, perpetually falling, even a stone is hollowed into a hole."
Thou washest away the things - Alluding to sudden falls of rain occasioning floods, by which the fruits of the earth are swept away; and thus the hope of man - the grain for his household, and provender for his cattle, is destroyed.