The Torah tells in Parashat Vayigash of the descent of Yaakov and his family to Egypt. Yosef reveals his identity to his brothers and then sends them back to Canaan to urge Yaakov to resettle in Egypt, where Yosef will care for him and spare him the ravages of the famine that had struck the region. Amidst his command to his brothers to bring Yaakov to Egypt, Yosef utters a somewhat peculiar sentence: "You can see for yourselves, and my brother Binyamin can see for himself, that it is indeed I who am speaking to you" (45:12). What exactly does Yosef mean, and how does this relate to the context at hand?
Rashi explains that Yosef senses his brothers' skepticism as to his identity and seeks to convince them. He shows them his berit mila and emphasizes the fact that he speaks lashon ha-kodesh (Hebrew). He adds that just as he harbors no ill will towards Binyamin, who did not participate in the sale, so has he no hard feelings towards them, either. Rashi's explanation does not, however, explain how this remark fits into context.
The Meshekh Chokhma suggests several different interpretations of the verse, all of which showing how this verse is included in Yosef's plea to his father to come down to Egypt. We present here the third and final explanation proposed by the Meshekh Chokhma. Yaakov may have preferred not to resettle in Egypt and to remain in Canaan, instead. (Indeed, he does not leave Canaan before receiving God's explicit blessing and promise that his offspring will return - 46:3-4; apparently, he was uneasy about this move outside his homeland.) He might have asked Yosef to simply send regular shipments of food and provisions from Egypt to support his father and his family in Canaan. Why must Yaakov move to Egypt? Anticipating this question, Yosef has his brothers impress upon his father "ki fi ha-medaber aleikhem" - literally, "that it is my mouth that speaks to you." Yosef has not become an Egyptian, despite his position of leadership in the country. Over these last, tumultuous twenty-two years, he has remained fully loyal to his heritage, to the teachings of Avraham, Yitzchak and Yaakov. It is still "my mouth" - the same Yosef as the one they sold - who speaks to the brothers. Therefore, regular communication with his foreign roots would undoubtedly trigger the suspicion and accusations of the native Egyptians over whom he rules. Given his refusal to abandon his prior cultural identification, establishing close ties with his family in Canaan would not be acceptable to the government and people of Egypt. Yaakov must therefore come to him.
This insightful analysis of the Meshekh Chokhma may shed some light on the famous question posed by the Ramban and others as to why Yosef did not notify Yaakov of his well-being immediately upon his rise to power in Egypt. Granted, his years in slavery and prison did not afford him the opportunity to send a postcard. But once he assumed the position of Egyptian viceroy, why did he not send a note home? We may perhaps suggest, in light of the Meshekh Chokhma's comments, that communicatiwith his father at that point was simply not feasible. Once he insisted on maintaining his Hebrew identity, the Egyptians would not allow him to make contact with his father in Canaan. Such contact would be acceptable only if Yaakov would resettle in Egypt. This presented Yosef with a considerable dilemma: what about his brothers? As far as he knows, they have no regret for what they did to him; they hate him and want nothing to do with him. Without question, under no circumstances would they willfully move to Egypt and come under Yosef's rule. Communication with Yaakov would therefore force Yaakov to decide between Yosef and the rest of the family. He would have to either abandon his ten children and reunite with Yosef in Egypt, or sever all ties with Yosef in order to remain with his brothers. Yosef wanted the family to stay together. Therefore, before summoning his family to Egypt, he ascertains that the brothers regret their mistreatment of him. As the Abarbanel famously explains, Yehuda's insistent appeal on Binyamin's behalf reflected the brothers' complete repentance for their sale of Yosef. Once this has been established, Yosef knew that having overcome their animosity towards him, the brothers would join Yaakov in Egypt, and he could thus invite his family to come under his care and survive the famine.