And he gave him the covenant of circumcision: and so Abraham begat Isaac, and circumcised him the eighth day; and Isaac begat Jacob; and Jacob begat the twelve patriarchs. He gave him the covenant of circumcision - That is, he instituted the rite of circumcision, as a sign of that covenant which he had made with him and his posterity. See Genesis 17:10, etc.
And so Abraham begat Isaac - Και οὑτως, And thus, in this covenant, he begat Isaac; and as a proof that he was born under this covenant, was a true son of Abraham and inheritor of the promises, he circumcised him the eighth day; and this rite being observed in the family of Isaac, Jacob and his twelve sons were born under the covenant; and thus their descendants, the twelve tribes, being born under the same covenant, and practising the same rite, were, by the ordinance of Gods legal inheritors of the promised land, and all the secular and spiritual advantages connected with it.