When Yosef’s brothers came to Egypt to purchase food during the years of famine, he recognized them immediately, but after 22 years of separation, they could not identify him. As a result, he was able to subject them to a dramatic series of events. After accusing them of being spies, he incarcerated Shimon to force them to return with his maternal brother Binyomin. After confusing them by inviting them to join him at a banquet, Yosef had his goblet planted in Binyomin’s sack to frame him for stealing.
When Yehudah earnestly pleaded for mercy, explaining how much their father Yaakov would suffer if they did not return with his beloved Binyomin, Yosef could not hold himself back anymore. He ordered all his Egyptian attendants to leave the room and revealed his true identity to his brothers. Rashi explains that Yosef verified his identity by showing them that he had a bris milah like them and speaking to them in their language of Lashon HaKodesh.
Rav Shimon Schwab notes that Yosef’s proof seems to be inadequate, as Rashi writes (41:55) that he instituted a law requiring all Egyptians to have bris milah in order to purchase food from the royal storehouse. Further, the Rambam rules (Hilchos Melochim 10:8) that descendants of Avraham from his wife Keturah are obligated to have bris milah. If so, what proof did Yosef’s bris milah provide when he could have been an Egyptian customer or one of Keturah’s offspring?
The Rambam writes (Moreh Nevuchim 3:8) that the Hebrew language is called Lashon HaKodesh because it does not contain crude words for certain activities and anatomical parts, which are always referred to euphemistically. Accordingly, the way a person speaks when conversing in Lashon HaKodesh reveals his level of tznius [modesty] and morality.
Thus, Rav Schwab suggests that Yosef did not physically expose himself to his brothers to demonstrate that he had a bris milah, as this would be highly inappropriate. Rather, Yosef spoke to them in Lashon HaKodesh to enable them to discern that although he had spent the past 22 years surrounded by the licentious culture of Egypt, he had remained true to his roots.
Rav Yisroel Reisman notes that this insight about the connection between a person’s speech in Lashon HaKodesh and his personal integrity explains why Pharaoh knew every language except Lashon HaKodesh (Rashi 50:6). Because he was so corrupt and depraved, he was physically incapable of speaking or even understanding such a holy language.
Similarly, when the Jewish people were exiled to Bavel, they adopted the Aramaic language in place of Lashon HaKodesh, which led them to fall and marry local non-Jewish women (Ezra 9:2, Nechemia 13:23-24). Rav Schwab adds that this connection also sheds light on the procedure known as metzitza b’peh [oral suctioning] during a bris milah, as these two parts of the body are profoundly linked, and the way a person speaks with his mouth reveals his commitment to modesty and virtue. (R’ Ozer Alport)
