Charles Ellicott Commentary Genesis 42:20

"and bring your youngest brother unto me; so shall your words be verified, and ye shall not die. And they did so." — Genesis 42:20 (ASV)

Bring your youngest brother. —Besides his desire to be reunited with his brother, Joseph reasonably felt that the possession of Benjamin would be the best means of inducing his father also to come to him. While substituting a much milder proposal for his former one, that nine should remain in prison, and the tenth go to fetch Benjamin, Joseph nevertheless takes care to make his brothers feel that he was in earnest.