Albert Barnes Commentary Psalms 77:18

"The voice of thy thunder was in the whirlwind; The lightnings lightened the world: The earth trembled and shook." — Psalms 77:18 (ASV)

The voice of thy thunder was in the heaven - Compare the notes at (Psalms 29:1–11). The word rendered “heaven” here—גלגל galgal—properly means “a wheel,” as of a chariot (Isaiah 5:28; Ezekiel 10:2, 10:6; Ezekiel 23:24; Ezekiel 26:10).

It then means a “whirlwind,” as that which rolls along (Ezekiel 10:13). It is also used to denote chaff or stubble, as driven along before a whirlwind (Psalms 83:13; Isaiah 17:13).

It is never used to denote heaven. It means here, undoubtedly, the whirlwind; and the idea is that in the ragings of the storm, or of the whirlwind, the voice of God was heard—the deep, bellowing thunder—as if God spoke to people.

The lightnings lightened the world - The whole earth seemed to be in a blaze.

The earth trembled and shook - See the notes at (Psalms 29:1–11).