‘Ten times’ is, says Barnes, to be understood loosely according to Hebrew custom. They have gone on and on pressing the point in spite of Job’s insistence that he is innocent.
All this scheming and deceit Satan understands for he is a cunning adversary, but he does not understand the grace and goodness of God for this is always beyond him. The believer by faith knows God better than the devil can ever know him. The devil no doubt has great intellect, but mere intellect is not enough to know God. By faith we come into a closeness of relationship with the Lord, from which the devil is forever shut out.