Psalms 104:9 - Joseph Benson’s Commentary on the Old and New Testaments

Thou hast set a bound Even the sand of the sea-shore, as is expressed Jeremiah 5:22. Which, though in itself contemptible, and a very poor defence to the earth against that swelling and raging element, yet, by God's almighty power and gracious providence, is made sufficient for that purpose, as the experience of five thousand years hath taught us. That they turn not again to cover the earth Once indeed they did, namely, in Noah's flood, because God commanded them so to do; but not since, because he prohibits them, having promised not to drown the world again. God himself glories in this instance of his power, and uses it as an argument with us to fear him, Job 38:8, &c.; Jeremiah 5:22. And surely this, if duly considered, would keep the world in awe of God and his goodness, that the waters of the sea would soon cover the earth if God did not restrain them.