הלוא זה אשר ישתה אדוני והוא נחש ינחש בו Is this not the one from which my master drinks, and from which he regularly divines?
The Torah describes Yosef’s framing of his brothers- by having the person in charge of his household place Yosef’s goblet in the bag of Binyamin so that Yosef could claim that Binyamin had stolen it. Many of the commentators offer explanations for what Yosef was trying to symbolize specifically with the cup, rather than any other object. The Ber Yosef (Rav Yosef Salant) suggests that Yosef was trying to awaken in them a feeling of guilt about their having sold him.
The Ber Yosef explains that the message Yosef was trying to convey was that although the brothers thought they were doing the right thing, they did not think about the effect that this was going to have on their father, Yaakov. Yosef was trying to remind them that, although he was one of the brothers, he was the main student of Yaakov. It was he who was called the בן זקונים, which Onkelus explains to mean that he was the wise son: the one who had absorbed all of the Torah knowledge that Yaakov had received in the study hall of Shem and Ever. The symbolism of the cup is that Torah is compared to wine. Therefore, Yosef had planted a cup that holds wine. The Gemara (Taanis7a) explains that while a student learns a lot from the teacher, the teacher learns even more from the students. This is similar to a cup of wine – one first pours the contents into a cup and then drinks from it. So, too, with a teacher to a student: the teacher first pours the Torah into the students and then drinks from the contents by gaining their wisdom. Yosef wanted the brothers to realize how much they had taken from Yaakov by removing his dedicated student.
Another concept to which Yosef was alluding by using the word “divines” was that Yaakov had received a sign from heaven. As long as none of his children died in Yaakov’s lifetime, he was guaranteed entrance to the world to come. By pretending that Yosef had been killed, they had taken away this comfort from their father. He was now uncertain of his place in the world to come. With these hints, Yosef hoped that his brothers would realize the mistake of their actions and regret what they had done.
We should also be attentive to the ramifications of our actions and to the hints people give us as we may have wronged them without even realizing it.