"And Yosef said to his brothers: 'Please come close to me'; and they approached. And he said: 'I am Yosef, your brother, whom you sold into Egypt'." (Bereshit 45:4)
Rashi comments that Yosef showed them that he was circumcised. This raises a difficulty: what kind of sign is that, if all the Egyptians were circumcised? For, as Rashi writes (42:55), from the first year of the famine, Yosef ordered them to be circumcised, and only on that condition did he provide them with food.
It can be answered that the Egyptians, when they circumcised themselves, did not fulfill the mitzvah of periah (פריעה: the uncovering of the glans following the circumcision of the foreskin), since the mitzvah of periah was only commanded to the People of Israel. Yosef, obviously, fulfilled the entire Torah and had the circumcision with periah, just as the Tosafot write (Yevamot 71b) that Abraham Avinu also practiced circumcision with periah, and so he did to his son Yitzchak on the eighth day, and so Yitzchak did to his son Yaakov, and Yaakov, in turn, to his twelve sons.
Furthermore, it can be said that Yosef gave them this sign because, one way or another, it constituted conclusive proof that he was truly Yosef. For if they did not know that the Egyptians had been circumcised, they would undoubtedly recognize him as Yosef upon seeing him circumcised like them. And if they did know that the Egyptians were circumcised, they surely also knew the reason: that, since he was the one who provided food to the entire population, he forced them to be circumcised to resemble him. From this, it necessarily follows that he was already circumcised beforehand. And if that were so, how could he be an Egyptian? He must perforce be Yosef, for if not, who would have forced him to be circumcised, he being the ruler over the entire land? It was he himself who established the decree of circumcision, and no one prior to him! In this way, it is an unmistakable sign that he was Yosef and not a mere Egyptian.
Zera Shimshon, Parashat Vayigash, Art. 4
