Albert Barnes Commentary Job 36:30

"Behold, he spreadeth his light around him; And he covereth the bottom of the sea." — Job 36:30 (ASV)

Behold, he spreadeth his light upon it - That is, upon His tabernacle or dwelling-place—the clouds. The allusion is to lightning, which flashes in a moment over the whole heavens. The image is exceedingly beautiful and graphic. The idea of “spreading out” the light in an instant over the whole of the darkened heavens is what Elihu had in his mind, and what impressed him so forcibly. Regarding the difficulty with the translation of the Septuagint here, see Schleusner on the word ἡδὼ hēdō.

And covereth the bottom of the sea - Margin, “roots.” The word “roots” is used to denote the bottom, as being the lowest part of a thing—as the roots of a tree. The meaning is that He covers the lowest part of the sea with floods of waters. Elihu’s object is to give an exalted conception of God’s greatness from the fact that His agency is seen in the highest and the lowest objects. He spreads out the clouds, thunders in His tabernacle, diffuses a brilliant light over the heavens, and at the same time is occupied in covering the bottom of the sea with the floods. He is Lord over all, and His agency is seen everywhere.

The highest and the lowest objects are under His control, and His agency is seen above and below. On the one hand, He covers the thick and dense clouds with light; and on the other, He envelops the depth of the ocean in impenetrable darkness.