This is a transitionary verse which moves from the quotation of a positive prophecy of the future state of those who believe, to the future state of those who will not believe. The reference to what Moses said is in Genesis 17: 14: “And the uncircumcised man child whose flesh of his foreskin is not circumcised, that soul shall be cut off from his people; he hath broken my covenant.”
It sets up the next quotation of scripture (verses 12–21 of this chapter), which quotes Micah 5:8–15.