Joseph issues a critical demand to his brothers, blending mercy with strict caution to set up a fateful test that will determine their future. The primary approach among commentators is that his requirement to bring their youngest brother is not about creating future trust, but about establishing the absolute truth. Bringing their brother to Egypt will retroactively validate their story, proving once and for all that they are honest men and not spies.
His warning regarding their survival carries a dual meaning, acting as both a threat and a promise. On one hand, it is a severe threat: if they fail to bring their brother, the accusation of espionage will be confirmed, and they will face execution. He even implies that his reach extends far enough to have them killed even if they manage to flee back to Canaan [ספורנו, אור החיים]. On the other hand, his words offer a promise of life. If they meet his condition, they will be saved from starvation, gaining the right to return to Egypt, trade freely, and securely purchase food at any time [שד״ל, אור החיים, ביאור שטיינזלץ].
The narrative notes that the brothers immediately complied, which raises a practical question, as they had not yet left for their journey to retrieve their youngest brother. Commentators offer three ways to understand what action they actually took at that very moment. One perspective is that they simply gave their verbal agreement. While they had completely rejected Joseph's initial, harsher proposal to leave all but one brother in prison, they now realized they had no other choice and accepted this new condition [חזקוני, ביאור יש״ר, רש״ר הירש].
Another approach views their response as a physical act of self-sacrifice. The brothers had to decide who would remain behind as a prisoner. Since Jewish law forbids handing over a single individual to death in order to save the group [העמק דבר], they collectively surrendered themselves to Joseph, offering him the choice to take whomever he wished [רבנו בחיי, צאינה וראינה]. A third viewpoint interprets their action as a purely spiritual one. Faced with severe distress, they did exactly what righteous people do: they engaged in deep soul-searching. They immediately confessed their guilt for selling their brother years earlier and accepted their current suffering as a fair and just punishment from God [שפתי כהן].