Albert Barnes Commentary Job 38:19

"Where is the way to the dwelling of light? And as for darkness, where is the place thereof," — Job 38:19 (ASV)

Where is the way where light dwelleth? Or, rather, where is the way or path to the place where light dwells? Light is conceived of as coming from a great distance and as having a place that might be regarded as its home.

It comes in the morning and is withdrawn in the evening. It seems as if it came from some far-distant dwelling-place in the morning to illuminate the world, and then retired to its home in the evening, thus making way for darkness to visit the earth.

The idea is this: “Do you know, when the light withdraws from the world, to what place it goes as its home? Can you follow it to its distant abodes and tell where they are? And when the shadows of night come forth and take its place, can you tell from where they come? When they withdraw again in the morning, can you follow them and tell where they are gathered together to remain?”

This thought is highly poetic and is not to be taken literally. The meaning is that God alone could know what the great fountain of light was and where it was.

Indeed, the question can essentially be asked of humanity with as much force and appropriateness now as in the time of Job. Who knows what the great fountain of light for the universe is? Who knows what light is? Who can explain the causes of its rapid flight from world to world? Who can tell what supplies it and prevents it from being exhausted? Who but God, after all the discoveries of science, can fully understand this?

And as for darkness, where is the place thereof? Darkness here is personified. It is represented as having a place of abode, as coming forth to take the place of light when that is withdrawn, and again as retiring to its dwelling when light reappears.