Romans 4:12-13

Romans 4:12-13. 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. 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.

For the law was not even given when that covenant promise was made. The law was 400 years afterwards. The covenant of grace was the oldest covenant of all, and it shall stand fast, whatever shall happen.