Albert Barnes Commentary Psalms 29:7

"The voice of Jehovah cleaveth the flames of fire." — Psalms 29:7 (ASV)

Divideth the flames of fire—Margin, “cutteth out.” The Hebrew word—חצב châtsab—properly means “to cut, to hew, to hew out;” as, for example, stones. The allusion here is undoubtedly to lightning; and the image is either that it seems to be cut out, or cut into tongues and streaks—or, more probably, that the “clouds” seem to be cut or hewed so as to make openings or paths for the lightning.

The eye is evidently fixed on the clouds and on the sudden flash of lightning, as if the clouds had been “cleaved” or “opened” for the passage of it. The psalmist's idea is that the “voice of the Lord,” or the thunder, seems to cleave or open the clouds for the flames of fire to play amidst the tempest. Of course, this language, as well as that which has already been noticed (Psalms 29:5), must be taken as denoting what appears to the eye, and not as a scientific statement of the reality in the case.

The rolling thunder not only shakes the cedars and makes the lofty trees on Lebanon and Sirion skip like a calf or a young unicorn, but it rends asunder or cleaves the clouds, and cuts out paths for the flames of fire.