Jamieson, Fausset and Brown on Job 9:8

8. spreadeth out--(Is 40:22; Psa 104:2). But throughout it is not so much God's creating, as His governing, power over nature that is set forth. A storm seems a struggle between Nature and her Lord! Better, therefore, "Who boweth the heavens alone," without help of any other. God descends from the bowed-down heaven to the earth (Psa 18:9). The storm, wherein the clouds descend, suggests this image. In the descent of the vault of heaven, God has come down from His high throne and walks majestically over the mountain waves (Hebrew, "heights"), as a conqueror taming their violence. So "tread upon" (De 33:29; Am 4:13; Mt 14:26). The Egyptian hieroglyphic for impossibility is a man walking on waves.