Abraham, he says, received circumcision as the seal of righteousness by faith, so that he might be father of all who believe. This is the same as the promise that he, or his seed, should be heir of the world. But take this circumstance, he seems to add, even separately from what came before, and again you will see that justification is possible only by faith.
The promise was given to Abraham, or to his seed, that he or it would be heir of the world. By virtue of what was this promise given? Was it by virtue of Abraham’s faithfulness to the law, or by virtue of his faith? The promise was not through the law, but through the righteousness of faith. The law did not yet exist then. Circumcision, which is the doorway into subjection to the law, did begin then. Yet faith preceded it and determined its meaning. The promise was given to faith, and circumcision, serving as a sign of faith, serves as a sign of the promise.
But if circumcision contributed nothing here, then much less did the law, which came long after circumcision. Therefore the promise was given by virtue of faith. What is the substance of the promise? That he should be heir of the world, meaning that he or his seed would inherit the world. In other words, the whole world would be his. It is self-evident that this possession could not be fleshly, but spiritual.
In what does it consist? This must be explained from the words of the promise: “In you and in your seed all nations shall be blessed.” Inheriting the world is the same as this blessing of all peoples. But what is this blessing itself? If we stand beside Abraham at the moment of the promise, its force will not be so clear to us. It is evident that something great and radiant is promised, but precisely what is not so clear. If, however, we look at how it was fulfilled, everything becomes clear.
The seed of Abraham is Christ, the Savior of the world. In Him are all the powers for life, piety, and eternal blessedness. The outpouring from Him of these powers upon the world is the blessing in Him. The nations are united to Him and draw this blessing from Him. But by being united to Him, they become His own, and through Him they also become Abraham’s own. For Christ the Lord is Abraham’s seed according to the flesh. This is Abraham’s inheritance of the world, or the blessing of the nations in Him.
By virtue of what is all this arranged? By virtue of faith. The promise was given to faith, and it is fulfilled by the action of faith. For people are united to the Lord and Savior, and receive blessing from Him, only by faith. Through faith, then, Abraham became father of all who believe, blesser of the nations, and heir of the world.
So clear to us, looking from this point, is the promise given to Abraham. Saint Paul intended to present it as clear by virtue of these concepts. He spoke, as it were, in this way: by faith Abraham was counted worthy of the great promise, and by faith it is now being brought to fulfillment. Therefore you Jews should not mix your law into this.
But the Jews could object: you present the matter perversely. It should be understood like this: Abraham, our forefather, indeed received the promise for faith, but afterward the law came, and the fulfillment of the promise must depend on subjection to the law. Only those who receive the law and submit to it can enter the sphere of Abraham’s promise. To this the Apostle answers: No. By this you destroy the promise.