Job 38:18 - Albert Barnes' Notes on the Bible

Hast thou perceived the breadth of the earth? - How far the earth extends. To see the force of this, we must remember that the early conception of the earth was that it was a vast plain, and that in the time of Job its limits were unknown. One of the earliest and most obvious inquiries would naturally be, What was the extent of the earth? By what was it bounded? And what was the character of the regions beyond those which were then known? All this was hidden from man at that time, and God, therefore, asks with emphasis whether Job had been able to determine this great inquiry. The knowledge of this is put on the same foundation as that of the depths of the sea, and of the dark regions of the dead, and in the time of Job the one was as much unknown as the other. God, who knew all this, must, therefore, be infinitely exalted above man.