Tafsiran Kejadian 17:11: Rashi, Bekhor Shor, Chizkuni & Sforno

ונמלתם AND YE SHALL CIRCUMCISE — This word, in spite of the נ in it, is not Niphal but the same as ומלתם and the נ in it is an addition to the root, which only sometimes appears in it, as, for example, the נ of נושך and of ונמלתם ;(נושא is Kal like ונשאתם “and ye shall carry” (Genesis 45:19), but יִמּוֹל (Genesis 17:12 and Genesis 17:13) is a Niphal form — “shall be circumcised” — like יֵעָשֶׂה “it shall be done”, and יֵאָכֵל “it shall be eaten”.

"And it will be a sign of the covenant between Me and you". A symbol and a sign that I am the Master and you are my servants, and the sign is sealed in a private place that will not be seen. The reason for this is so that the (non-Jewish) nations of the world won't say that the Jews are blemished ("ba'alei mumin"). And since the Holy One, Blessed be He, commanded men and not women, we learn that the place of manhod ("makom zachrut") was where God commanded to seal the covenant. And the blood of niddah that women guard, and tell their openings to their husbands, this is to them the blood of the covenant ("dam brit").

ונמלתם, “you shall circumcise yourselves;” all those who had not been circumcised on the eighth day after birth.