13 For not through law was the promise to Abraham, or to his seed, that he should be heir of the world, but through the righteousness of faith.
Romans 4:13 Cross References - ABU
Romans 9:8
8 That is, not they who are the children of the flesh are children of God; but the children of the promise are reckoned as seed.
Galatians 3:16-18
16 Now to Abraham were the promises spoken, and to his seed. He says not, and to seeds, as concerning many; but as concerning one, and to thy seed, which is Christ.
17 But this I say, that a covenant before confirmed by God, the law, which came four hundred and thirty years after, does not annul, to make the promise of no effect.
18 For if the inheritance is of law, it is no more of promise; but God has freely given it to Abraham by promise.
Galatians 3:29
29 And if ye are Christ's, then are ye Abraham's seed, heirs according to the promise.