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.
Forbidden relationships in Judaism
The classical rabbis saw 18 as the ideal age to become married, and anyone unmarried after the age of twenty was said to have been cursed by God; rabbinical courts frequently tried to compel an individual to marry, if they had passed the age of twenty without marriage. Nevertheless, the classical rabbis viewed study of the Torah as a valid reason for remaining unmarried, although they were only rarely willing to regard life-long celibacy favourably. Since the classical rabbis viewed marriage as a duty deriving from the instruction to "go forth and multiply", they also believed that the duty to marry ended once the husband had fathered both a son and a daughter; despite this, they also argued that no man should live without a wife even after he has several children.