Romans 4:11-16   11. And he received the sign of circumcision, a seal of the righteousness of the faith which he had yet being uncircumcised: that he might be the father of all them that believe, though they be not circumcised; that righteousness might be imputed unto them also: 12. And the father of circumcision to them who are not of the circumcision only, but who also walk in the steps of that faith of our father Abraham, which he had being yet uncircumcised. 13. For the promise, that he should be the heir of the world, was not to Abraham, or to his seed, through the law, but through the righteousness of faith. 14. For if they which are of the law be heirs, faith is made void, and the promise made of none effect: 15. Because the law worketh wrath: for where no law is, there is no transgression. 16. Therefore it is of faith, that it might be by grace; to the end the promise might be sure to all the seed; not to that only which is of the law, but to that also which is of the faith of Abraham; who is the father of us all,

Romans 9:6-8   6. Not as though the word of God hath taken none effect. For they are not all Israel, which are of Israel: 7. Neither, because they are the seed of Abraham, are they all children: but, In Isaac shall thy seed be called. 8. That is, They which are the children of the flesh, these are not the children of God: but the children of the promise are counted for the seed.