Genesis 42:15, commentary and pictures

Hereby ye shall be proved is an oath sworn by the life of Pharaoh that the brothers shall not go forth from Egypt unless their youngest brother comes there. It is a demand for proof of their account that they are honest men who came only to buy food, that they were twelve brothers with the youngest left at home, in order to establish whether their words are true. It bars them from leaving and holds them confined until that youngest brother, Benjamin, is brought to Egypt.

One of them is to go to fetch Benjamin while the rest remain behind, and refusal will be taken as proof that they are spies. Beyond mere verification, the demand is meant to draw out information about his father and what has become of Benjamin, and to learn whether the brothers still have the same haughty spirit as when he lived with them. The brothers meet the test humbled in adversity, with grief rather than anger at the suspicion cast upon them.

The test makes them fear death or slavery and leads them to reflect on their cruelty to Joseph and their guilt before God.