Circumcision
Circumcision is very important to most branches of Judaism, with over 90% of male adherents having the procedure performed as a religious obligation. The basis for its observance is found in the Torah of the Hebrew Bible, in Genesis chapter 17, in which a covenant of circumcision is made with Abraham and his descendants. Jewish circumcision is part of the "brit milah" ritual, to be performed by a specialist ritual circumciser, a "mohel", on the eighth day of a newborn son's life, with certain exceptions for poor health. Jewish law requires that the circumcision leaves the glans bare when the penis is flaccid. Converts to Conservative and Orthodox Judaism must also be circumcised; those who are already circumcised undergo a symbolic circumcision ritual. Circumcision is not required by Judaism for one to be considered Jewish, but some adherents foresee serious negative spiritual consequences if it is neglected.
Isaac
In rabbinical tradition, the age of Isaac at the time of binding is taken to be 37, which contrasts with common portrayals of Isaac as a child. The rabbis also thought that the reason for the death of Sarah was the news of the intended sacrifice of Isaac. The sacrifice of Isaac is cited in appeals for the mercy of God in later Jewish traditions. The post-biblical Jewish interpretations often elaborate the role of Isaac beyond the biblical description and primarily focus on Abraham's intended sacrifice of Isaac, called the "aqedah" ("binding"). According to a version of these interpretations, Isaac died in the sacrifice and was revived. According to many accounts of Aggadah, unlike the Bible, it is Satan who is testing Isaac as an agent of God. Isaac's willingness to follow God's command at the cost of his death has been a model for many Jews who preferred martyrdom to violation of the Jewish law.