Albert Barnes Commentary Job 38:25

"Who hath cleft a channel for the waterflood, Or the way for the lightning of the thunder;" — Job 38:25 (ASV)

Who has divided a watercourse for the overflowing of waters – That is, for the waters that flow down from the clouds. The idea seems to be this: the waters of heaven, instead of pouring down in floods or all coming down together, seemed to flow in certain canals formed for them, as if they had been cut out through the clouds for that purpose. The causes of rain, the manner in which water was suspended in the clouds, and the reasons why the rain did not come down altogether in floods, early attracted attention and prompted investigation. The subject is referred to more than once in this book; see the notes at (Job 26:8).

Or a way for the lightning of thunder – For the thunder-flash. The idea is this: a path seems to be opened in the dark cloud for the passage of the lightning flash. How such a path was made, by what agency or by what laws, was the question for inquiry. The lightning seemed to burst suddenly through the dark cloud, where there was no opening and no sign of a path before, and to pursue its zig-zag journey as if all obstructions were removed and it passed over a beaten path. The question is, who could have traced out this path for the thunder-flash to follow? Who could do it but the Almighty? And still, with all the light that science has shed on the subject, we may repeat the question.