Psalms 18:12 - Joseph Benson’s Commentary on the Old and New Testaments

At the brightness that was before him, &c. Schultens, Waterland, and some others, translate this verse, At his lightning, his clouds swelled and burst out into hail-stones and balls of fire. The meaning is, that through the lightning his clouds fermented, that is, swelled, and, as it were, boiled over, being rarefied by the heat. In the former part of this description, the clouds are represented as condensed, heavy, and lowering, ready to burst out with all the fury of a tempest; and here, as beginning to disburden and discharge themselves, by the eruption of the lightning in fire, flames, and hail-stones mixed. The abrupt manner in which the burning coals and hail-stones are mentioned, points out the sudden and impetuous fall of them. The words rendered coals of fire here signify living, burning coals. Where the lightning fell it devoured all before it, and turned whatever it touched into burning embers. See Chandler and Dodd.