To neglect circumcision (b’rit milah) is to neglect the chosen sign of the covenant, and consequently, it is rejection of the covenant itself. It was to become a unique marker, outwardly identifying those males of the offspring of Avraham, as inheritors of the magnificent promises that HaShem was making with this man. It does not serve to secure those promises through personal effort. What is more, the sign of circumcision was to be an indicator that the participant was adopting the same faith that Avraham possessed! The promises were of faith (read Romans chapter 4 carefully). To be 100% sure, the Torah says that the promises were given to him before he was circumcised (Ibid. 10, 11)! This is why, after HaShem promised that his seed would be as numerous as the stars (15:5, 6), Avraham was credited with being righteous—because he believed the unbelievable!