Charles Ellicott Commentary Job 37:4

"After it a voice roareth; He thundereth with the voice of his majesty; And he restraineth not [the lightnings] when his voice is heard." — Job 37:4 (ASV)

After it a voice roars — i.e., the thunderclap that follows the lightning-flash.

And He stays them not (or will not restrain them) when His voice is heard. —What does this mean? We understand it, “Yet no one can track them (i.e., the thunder and the lightning) when His voice is heard. They travel in paths that no one can explore. Vivid as the lightning is, who can pursue its course?”