In his discussion of the rites of circumcision, Maimonides (Guide of the Perplexed, Part 3, Chapter 49) explains that there are three reasons behind the practice. First, circumcision is a common sign uniting those who share the Jewish faith. This common identifier creates a bond of mutual love and assistance. Second, the very act of circumcision is an affirmation of faith. Judaism demands more of its adherents than the profession of a creed. Judaism requires a sacrifice of the flesh. Third, and perhaps most important, is the fact that for most Jews circumcision represents entry into the covenant that God struck with Abraham.
Even though he makes the link between circumcision and the Abrahamic covenant, Maimonides cites Leviticus 12:3 as the scriptural source for circumcision rather than the more obvious verse in the Book of Genesis (17:12) where circumcision is first mentioned in connection with the covenant of Abraham. In fact, other medieval authorities are unanimous in ascribing the commandment of circumcision to Genesis 17:12 (see, for example, Sefer Ha-Hinukh, 2). Curiously, however, Maimonides says that the command to circumcise all Jewish males stems from the five Hebrew words of the Book of Leviticus rather than the lofty covenant described in Genesis.
Yeshayahu Leibowitz, less known but equally as scholarly as his better-known sister Nehama, addresses this enigma. Professor Leibowitz believes that Maimonides choice of scriptural source has profound significance in terms of faith. In his short but provocative book entitled Notes and Remarks on the Weekly Parashah, Prof. Leibowitz writes: “What obligates us in terms of faith are only those mitzvot which were given at Sinai and thereafter. The worship of God through the mitzvot is not a remembrance of ancient times, as claimed by some today who wish to explain their significance as symbolic…It is true that we are entering the child into the covenant of our father Abraham, but not because there was a covenant made between Abraham and God – or vice versa…but because we were commanded to enter the child into the covenant of our father Abraham.”
“The worship of God,” he goes on to say, “is not folklore, even in the most profound sense. It is not a remembrance of what was, of what happened to the Jewish people and of what happened to our forefathers. The worship of God means fulfilling the commandments which were given to us.”