Psalms 18:9 - Joseph Benson’s Commentary on the Old and New Testaments

He bowed the heavens By producing thick and dark clouds, by which the heavens seemed to come down to the earth; and came down Not by change of place, but by the manifestation of his presence and power on my behalf. In other words, he, as it were, made the heavens bend under him, when he descended to take vengeance on his and my enemies. And darkness was under his feet The psalmist seems here to express the appearance of the Divine Majesty in a glorious cloud, descending from heaven, which, underneath, was substantially dark, but above bright, and shining with an amazing lustre; and which, by its gradual descent, would appear as if the heavens themselves were bending down and approaching toward the earth.