15 But in this way will you be put to the test: by the life of Pharaoh, you will not go away from this place till your youngest brother comes here. 16 Send one of your number to get your brother, and the rest of you will be kept in prison, so that your words may be tested to see if you are true; if not, by the life of Pharaoh, your purpose is certainly secret.
Matthew Henry's Commentary on Genesis 42:15-16
Commentary on Genesis 42:7-20
(Read Genesis 42:7-20)
Joseph was hard upon his brethren, not from a spirit of revenge, but to bring them to repentance. Not seeing his brother Benjamin, he suspected that they had made away with him, and he gave them occasion to speak of their father and brother. God, in his providence, sometimes seems harsh with those he loves, and speaks roughly to those for whom yet he has great mercy in store. Joseph settled at last, that one of them should be left, and the rest go home and fetch Benjamin. It was a very encouraging word he said to them, "I fear God;" as if he had said, You may be assured I will do you no wrong; I dare not, for I know there is one higher than I. With those that fear God, we may expect fair dealing.