Biblically, it was a mark for two purposes: First to show separation and distinction from those not following God - because in those days, nobody would think to cut the foreskin from the penis of an heir - these were supposed to be “slaves” of God. Second, it was intended to decrease sexual sensitivity among the followers of God, reminding them that their purpose was not the body, but the Spirit, and that their ultimate means of reproducing was not copulation, but to bear witness to the One True God as the light of Heaven among those who walked away. The result, however, was that the children of God became children of Satan, and supplemented their reduced sensitivity with greater perversion, and today push male circumcision as a method of increasing perversion among the goyim.