Albert Barnes 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. To show that the faith of Abraham, on which his justification depended, was not by the law, the apostle proceeds to show that the promise concerning which his faith was so remarkably demonstrated was before the law was given. If this was so, then it was an additional important consideration in opposition to the Jew, showing that acceptance with God depended on faith, and not on works.

That he should be the heir of the world. An heir is one who succeeds, or is to succeed, to an estate. In this passage, the world, or the entire earth, is regarded as the estate to which reference is made; and the promise is that the descendants of Abraham should succeed to that, or should possess it as their inheritance.

The precise expression used here, "heir of the world," is not found in the promises made to Abraham. Those promises were: that God would make of him a great nation (Genesis 12:2); that in him all the families of the earth should be blessed (Genesis 12:3); that his posterity should be as the stars for multitude (Genesis 15:5); and that he should be a father of many nations (Genesis 17:5).

As this latter promise is one to which the apostle particularly refers (Romans 4:17), it is probable that he had this in mind. This promise, at first, referred to his numerous natural descendants and to their possessing the land of Canaan. But it is also regarded in the New Testament as extending to the Messiah (Galatians 3:16) as his descendant, and to all his followers as the spiritual seed of the father of the faithful. When the apostle calls him "the heir of the world," he sums up in this comprehensive expression all the promises made to Abraham, intimating that his spiritual descendants, that is, those who possess his faith, will yet be so numerous as to possess all lands.

Or to his seed. To his descendants.

Through the law. By the observance of the law; or made as a result of observing the law; or depending on the condition that he should observe the law. The covenant was made before the law of circumcision was given and long before the law of Moses . It was therefore independent of both.

But through the righteousness of faith. As a result of, or in connection with, the strong confidence that he showed in the promises of God (Genesis 15:6).