Albert Barnes Commentary Job 38:4

"Where wast thou when I laid the foundations of the earth? Declare, if thou hast understanding." — Job 38:4 (ASV)

Where were you when I laid the foundations of the earth? — The first appeal is to the creation. The question here, “Where were you?” implies that Job was not present. He did not exist then. He could not, therefore, have aided God, or counseled Him, or understood what He was doing. How presumptuous, therefore, it was for one so short-lived to sit in judgment on the doings of Him who had formed the world! How little could he expect to be able to know of Him!

The expression, “laid the foundations of the earth,” is taken from building an edifice. The foundations are first laid, and the superstructure is then reared. It is a poetic image and is not designed to give any intimation about the actual process by which the earth was made or the manner in which it is sustained.

If you have understanding — Margin, as in Hebrew, “if you know.” That is, “Declare how it was done. Explain the manner in which the earth was formed and fixed in its place, and by which the beautiful world grew up under the hand of God.” If Job could not do this, what presumption it was for him to speak as he had done of the divine administration!