Genesis 42:7

knew them Joseph at once recognized his brethren. They did not recognize him. From a boy he had become a man; they were grown men when they sold him, and were comparatively unaltered. He in stature, dress, hair, and ornament must have been wholly changed from the rough shepherd lad of Canaan. According to E (Genesis 41:1; Genesis 41:47) more than nine years, according to P (Genesis 37:2; Genesis 41:46) more than twenty years had elapsed, since he had been separated from his home in Canaan.

made himself strange In order to account for Joseph's treatment of his brethren, the two most common explanations have been that he sought (1) to prove them, and (2) to punish them. His motives were, doubtless, mixed. The welfare of his father and of his own brother is uppermost in his thoughts. As he does not see them, he doubts whether the brethren who had treated him so shamefully will have maintained any regard for the life of his aged father or his young brother. He assumes a tone of harshness which he does not feel; and suffers a vein of generous hospitality and munificence to mingle with severity in the treatment of his brethren, so as to add to their mystification and confusion.