בראשית, פרק מ״ד, פסוק ב׳

The planting of a special cup in Benjamin's sack marks the climax of a carefully calculated plan, designed to put the brothers through a fateful trial. The object used was not an ordinary drinking vessel, but an exceptionally long or large cup [אבן עזרא, רש״י, מזרחי, מחוקקי יהודה]. It was specifically made of silver, a metal that was sometimes rarer and more valuable than gold in ancient Egypt because it had to be imported from other lands [פענח רזא, ביאור שטיינזלץ]. Alternatively, the phrasing of the story suggests that two distinct vessels were actually hidden in the sack: Joseph's personal gold cup alongside an additional silver cup that he valued less [פענח רזא]. From a literary perspective, once the cup is explicitly mentioned, its specific name vanishes from the rest of the story. It is replaced by generic terms, as though the word itself is concealed within the text just as the physical cup was hidden inside the sack [ברכת אשר על התורה].

The primary approach among commentators is that this act was a deep psychological and moral test. Joseph sought to discover if his brothers truly regretted selling him years earlier. By placing Benjamin, Rachel's second son, in danger of slavery, Joseph tested whether the brothers would risk their own lives to save him, thereby correcting their past sin, or if they would simply abandon him to his fate as they had done before [ספורנו, חומש קה״ת]. Another perspective suggests a different motive: Joseph had left Benjamin as a young child and did not actually recognize him. Suspecting that the brothers might have brought a random youth from the marketplace, Joseph designed this test to verify the boy's identity. If the brothers fought to protect him, it would prove he was indeed their true brother [חזקוני].

The plot also involved returning the money the brothers had paid for their grain. This detail was crucial to ensure they would not simply dismiss Benjamin as a common thief. When the brothers discovered that everyone's money had been returned, they would realize they were the targets of a deliberate conspiracy orchestrated by the Egyptian ruler. Recognizing this setup would compel them to stand and fight for Benjamin rather than abandon him under the assumption that he was guilty of a crime [ביאור יש״ר].

A natural question arises regarding how Joseph could inflict such distress on his beloved innocent brother. A surprising explanation reveals that there may have been a secret, prearranged agreement between Joseph and Benjamin. According to this line of thought, Joseph had already privately revealed his true identity to Benjamin and shared the details of the impending test. Because of this secret alliance, the instruction to plant the cup was not a harsh command, but rather a statement of fact regarding a mutual plan that had already been agreed upon by both brothers [הכתב והקבלה, ביאור יש״ר].