Divrei Torah on the weekly portions
"And Yosef said to his brothers: please step near to me, and they stepped near. And he said: I am Yosef your brother whom you sold to Egypt" (Bereishit 45:4).
Rashi quotes the Midrash (Bereishit Rabbah 93:11) that Yosef showed his brothers that he was circumcised, proving he was indeed Yosef.
Kli Yakar cites the beautiful Midrash (VaYikra Rabbah 32:5, well worth reading on Pesach) which states that the Israelites were redeemed from Egypt in the merit of four deeds:
When Yosef revealed himself to his brothers, he requested that they return to Israel to bring Yaakov and the family down to Egypt. Yosef wished to show them, at the commencement of the Egyptian exile, in what merit they would be redeemed.
The first point he stressed was "I am Yosef". Although Pharaoh had given him an Egyptian name Tzofnat Paneach (Bereishit 41:45), he stressed that he had no regard for that name and he was still called Yosef.
A few verses later (Bereishit 45:12) he urged them to pay attention that "my mouth is speaking to you". The Midrash (Bereishit Rabbah 93:11) explains that he was speaking to them in Hebrew and not in Egyptian. He had retained his Jewish language.
He showed them that he was circumcised and had not undergone any surgical procedure to appear like an Egyptian. This demonstrated his high moral standard even amongst the depraved Egyptian society where he lived.
And finally by saying to his brothers "Step near to me", he demonstrated his love for them that he wished to be close to his brothers. He asked them to step near to him when he spoke about their selling him so that Binyamin should not hear. Additionally, he never told Yaakov what the brothers had done. This accentuated how careful Yosef was not to slander his brothers, which was the fourth point in which they merited to be redeemed.