Circumcision is the oldest Jewish ritual. Abraham circumcised himself, and his son Yitzchak, as a sign of God's covenant with him and his children, and we have been doing it to eight-day old Jewish boys ever since. Circumcision teaches us that we are partners in creation with God. Human beings are not perfect, and need to be perfected with the brit, the covenant of circumcision. If a baby is ill, the brit is postponed until he is better, otherwise, the brit is done on the eight day, even if it is a Shabbat or holiday. Although there is some argument on the subject, circumcision is still seen by many doctors and experts as being beneficial from a health perspective.