From where do we know that the Bris Milah must be performed on the male organ?
Rashi and Ramban #1: From the words "Arel Zachar", which connote the part of the body that distinguishes between a male and a female. 1
Ramban #2 (citing the Ibn Ezra): "Orlaso" (S'tam) refers to the location of the Ervah.
Ramban #3: "B'sar Orlaschem" (in Pasuk 11) implies that one cuts off the flesh that covers a limb, and the only location on the body that fits that description is 'the flesh that covers the crown (of the male organ).
Seforno: The word "bi'Vesarchem" (in the previous Pasuk) is a refined word for the male organ. 2
Orlos of other locations are always specific - such as Orlas Lev and Orlas Sefasayim).
As we find in Yechezkel (16:26) and in other places.
Why does the Torah designate specifically the male organ for the Mitzvah of Bris Milah?
Seforno (Pasuk 13): Because it is the limb that is responsible for eternity, which Bris denotes, and because it is the limb that creates the children, on whom the Bris includes. 1
As in Pasuk 10.
When the Pasuk sentences someone who fails to perform the Bris Milah to Kareis, to whom is it referring?
Rashi: It is referring to the child himself, whose father did not perform the Mitzvah, and who now becomes Bar-Mitzvah. 1
A father who fails to perform the Mitzvah transgresses an Asei but is not subject to Kareis.
What is the definition of Kareis?
Rashi: It means that the sinner will die childless, before his allotted time. 1
See Sifsei Chachamim.
רש"י: כאן למד שהמילה באותו מקום שהוא ניכר בין זכר לנקבה: אולי בא הפסוק ללמד שהמילה היא בזכר ולא ללמד היכן המילה?
גור אריה: כבר כתוב (בפסוק י) "המול לכם כל זכר" ומה בא ללמדינו כאן? אלא שהמילה במקום שמבדיל בין זכר לנקבה.
רש"י: ונכרתה הנפש- הולך ערירי ומת קודם זמנו: מה משמעות "ערירי" וכיצד נלמד מהפסוק?
גור אריה: ערירי פירושו ללא וולד, ולמדו זאת מ'נכרת' כי משמעו נכרת מהשורש, וכשיש בנים אין זה כריתות שהרי הענפים נמשכים מהשורש.
