Albert Barnes Commentary Job 28:26

"When he made a decree for the rain, And a way for the lightning of the thunder;" — Job 28:26 (ASV)

When He made a decree for the rain - This refers to a statute or law (חק chôq) by which the rain is regulated. It is not sent by chance or haphazardly; it operates under regular and settled laws. We cannot suppose that these laws were understood in the time of Job, but it might have been understood that the rain was regulated by laws, and this fact would show that God was qualified to impart wisdom. His kingdom was one of settled law and not of chance or caprice, and if the rain was regulated by statute, it was fair to presume that He did not deal with His people by chance, and that afflictions were not sent without rule (Compare to the notes at Job 5:6).

And a way - A path through which the rapid lightning should pass - referring, perhaps, to the apparent “opening” in the clouds in which the lightning seems to move along.

The lightning of the thunder - The word “lightning” here (חזיז chăzı̂yz) properly means “an arrow,” from הזז hāzaz — obsolete, meaning to pierce through, to transfix, or to perforate; and hence, it refers to lightning due to the rapidity with which it passes - like an arrow. The word “thunder” (קולות qôlôt) means “voices,” and thus “thunder,” as being preeminently the voice of God . The whole expression here means “the thunder-flash.” Coverdale renders this, “when he gave the mighty floods a law;” but it undoubtedly refers to the thunderstorm. The central idea is that He who controls the rapid lightning, regulating its laws and directing its path through the heavens, is qualified to communicate truth to people and can explain the great principles on which His government is administered.