A Commentary, Critical, Practical, and Explanatory on the Old and New Testaments, by Robert Jamieson, A.R. Fausset and David Brown  at sacred-texts.com
gen 42:1JOURNEY INTO EGYPT. (Gen. 42:1-38)
Now when Jacob saw that there was corn in Egypt--learned from common rumor. It is evident from Jacob's language that his own and his sons' families had suffered greatly from the scarcity; and through the increasing severity of the scourge, those men, who had formerly shown both activity and spirit, were sinking into despondency. God would not interpose miraculously when natural means of preservation were within reach.
gen 42:5the famine was in the land of Canaan--The tropical rains, which annually falling swell the Nile, are those of Palestine also; and their failure would produce the same disastrous effects in Canaan as in Egypt. Numerous caravans of its people, therefore, poured over the sandy desert of Suez, with their beasts of burden, for the purchase of corn; and among others, "the sons of Israel" were compelled to undertake a journey from which painful associations made them strongly averse.
gen 42:6Joseph was the governor--in the zenith of his power and influence.
he it was that sold--that is, directed the sales; for it is impossible that he could give attendance in every place. It is probable, however, that he may have personally superintended the storehouses near the border of Canaan, both because that was the most exposed part of the country and because he must have anticipated the arrival of some messengers from his father's house.
Joseph's brethren came, and bowed down themselves before him--His prophetic dreams [Gen 37:5-11] were in the course of being fulfilled, and the atrocious barbarity of his brethren had been the means of bringing about the very issue they had planned to prevent (Isa 60:14; Rev 3:9, last clause).
gen 42:7Joseph saw his brethren, and he knew them, . . . but they knew not him--This is not strange. They were full-grown men--he was but a lad at parting. They were in their usual garb--he was in his official robes. They never dreamt of him as governor of Egypt, while he had been expecting them. They had but one face; he had ten persons to judge by.
made himself strange unto them, and spake roughly--It would be an injustice to Joseph's character to suppose that this stern manner was prompted by any vindictive feelings--he never indulged any resentment against others who had injured him. But he spoke in the authoritative tone of the governor in order to elicit some much-longed-for information respecting the state of his father's family, as well as to bring his brethren, by their own humiliation and distress, to a sense of the evils they had done to him.
gen 42:9Ye are spies--This is a suspicion entertained regarding strangers in all Eastern countries down to the present day. Joseph, however, who was well aware that his brethren were not spies, has been charged with cruel dissimulation, with a deliberate violation of what he knew to be the truth, in imputing to them such a character. But it must be remembered that he was sustaining the part of a ruler; and, in fact, acting on the very principle sanctioned by many of the sacred writers, and our Lord Himself, who spoke parables (fictitious stories) to promote a good end.
gen 42:15By the life of Pharaoh--It is a very common practice in Western Asia to swear by the life of the king. Joseph spoke in the style of an Egyptian and perhaps did not think there was any evil in it. But we are taught to regard all such expressions in the light of an oath (Mat 5:34; Jam 5:12).
gen 42:17put them . . . into ward three days--Their confinement had been designed to bring them to salutary reflection. And this object was attained, for they looked upon the retributive justice of God as now pursuing them in that foreign land. The drift of their conversation is one of the most striking instances on record of the power of conscience [Gen 42:21-22].
gen 42:24took . . . Simeon, and bound him--He had probably been the chief instigator--the most violent actor in the outrage upon Joseph; and if so, his selection to be the imprisoned and fettered hostage for their return would, in the present course of their reflections, have a painful significance.
gen 42:25Joseph commanded to fill their sacks with corn, and to restore every man's money--This private generosity was not an infringement of his duty--a defrauding of the revenue. He would have a discretionary power--he was daily enriching the king's exchequer--and he might have paid the sum from his own purse.
gen 42:27inn--a mere station for baiting beasts of burden.
he espied his money--The discovery threw them into greater perplexity than ever. If they had been congratulating themselves on escaping from the ruthless governor, they perceived that now he would have a handle against them; and it is observable that they looked upon this as a judgment of heaven. Thus one leading design of Joseph was gained in their consciences being roused to a sense of guilt.
gen 42:35as they emptied their sacks, that, behold, every man's . . . money was in his sack--It appears that they had been silent about the money discovery at the resting-place, as their father might have blamed them for not instantly returning. However innocent they knew themselves to be, it was universally felt to be an unhappy circumstance, which might bring them into new and greater perils.
gen 42:36Me have ye bereaved--This exclamation indicates a painfully excited state of feeling, and it shows how difficult it is for even a good man to yield implicit submission to the course of Providence. The language does not imply that his missing sons had got foul play from the hands of the rest, but he looks upon Simeon as lost, as well as Joseph, and he insinuates it was by some imprudent statements of theirs that he was exposed to the risk of losing Benjamin also.
gen 42:37Reuben spake, . . . Slay my two sons, if I bring him not to thee--This was a thoughtless and unwarrantable condition--one that he never seriously expected his father would accept. It was designed only to give assurance of the greatest care being taken of Benjamin. But unforeseen circumstances might arise to render it impossible for all of them to preserve that young lad (Jam 4:13), and Jacob was much pained by the prospect. Little did he know that God was dealing with him severely, but in kindness (Heb 12:7-8), and that all those things he thought against Him were working together for his good.