There is considerable debate as to why God would choose circumcision to mark the covenant between himself and Abraham and Abraham's descendants. One can only speculate as to why this particular rite was chosen. The best explanation I have heard as that it marks the source of the beginning of life. Hence, if one is a member of the covenant, that is one of the chosen people, he is marked as a member of those chosen people at the moment of his conception. Interestingly, there is no equivalent provision for marking or identifying female children. Since early Hebrew society was male oriented, it would appear that the male, as head of the household, represented the dedication of the entire household to the covenant between God and Abraham and his descendants.