Or HaChaim on Genesis 44:1/אור החיים על בראשית מ״ד:א׳

1אמתחת הקטון מלא את אמתחות האנשים אכל…ואת גביעי תשים בפי. "Fill up the pouches of these men with food and place my goblet in the pouch of the youngest." We need to understand Joseph's motivations in all this. We can hardly assume that he wanted to cause his brothers anguish after he had invited them to his palace and had wined and dined them. Perhaps Joseph had three separate motivations. 1) He wanted that they should be able to atone for having stolen him at the time. By accusing them of theft they would feel the embarassment a thief feels when he has been found out. Once they experienced this feeling they could atone for the sale of Joseph. 2) He wanted to find out if the brothers would risk their lives for the freedom of Benjamin. This would enable him to gauge the degree of brotherliness they felt towards Benjamin. This in turn would enable Joseph to forgive them their sin against him. 3) He sent them a signal that there was somebody in the viceroy's palace who was thoroughly familiar with their past history. He had already made them curious about this on the previous day when he had seated them according to their respective ages at lunch (43,33).