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 evinced 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 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 posterity 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 (see Romans 4:17), it is probable that he had this in his eye. This promise had, at first, respect 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, shall yet be so numerous as to possess all lands.
Or to his seed - To his posterity, or descendants.
Through the law - By the observance of the Law; or made in consequence 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 (compare Galatians 3:16-18), and was independent of both.
But through ... - In consequence of or in connection with the strong confidence which he showed in the promises of God, Genesis 15:6.