Charles Spurgeon Commentary Romans 4:13

"For not through the 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 (ASV)

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.

The law was promulgated on Mount Sinai four hundred years after the covenant of grace was made with Abraham the father of believers, and so made with all believers, for they are his true seed, and God has entered into a covenant of grace and salvation with them.