And God said to Abraham, “As for you, you must keep my covenant, you and your seed after you throughout their generations. This is my covenant ... every male of yours must be circumcised. When you circumcise your foreskin flesh, it will become a covenant sign between me and you. Throughout your generations, each male of yours must be circumcised when he is eight days old ... And my covenant will be in your flesh as an eternal covenant.
In many human societies, group membership is marked with a special costume—whether a kilt, a sari, a military uniform, a navy blue suit or a black yarmulke. Even in societies that wear minimal clothing, status and affiliation can be conveyed by special tokens and ornaments. But these, like garments, can be removed at will.
Permanent scarification and tattooing are more permanent and presumably more ancient methods to mark membership. Because these operations are painful, submitting to them constitutes a true rite of passage. Stoically undergoing the ordeal demonstrates mature self-discipline and seriousness of purpose. Ever after, one carries a life-long “membership card” engraved on one’s body.