וּנְמַלְתֶּ֕ם אֵ֖ת בְּשַׂ֣ר עָרְלַתְכֶ֑ם וְהָיָה֙ לְא֣וֹת בְּרִ֔ית בֵּינִ֖י וּבֵינֵיכֶֽם׃
너희는 양피를 베어라 이것이 나와 너희 사이의 언약의 표징이니라
Rashi on Genesis
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”.
Sforno on Genesis
לאות ברית, as a constant reminder to walk in His paths. The sign of the circumcision is to be like the stamp on the skin of a slave identifying him as belonging to a certain master.
Radak on Genesis
ונמלתם, this is the positive commandment to the father to circumcise his male child, or to the son to perform circumcision on himself when he reaches the age of manhood if it has not been performed on him before then by the court.