Paul says that the promise given to Abraham that he should inherit the world did not come from the law but by faith, which was reckoned to him as righteousness. It doubtless follows that everyone who hopes that God’s righteousness will be imputed to him hopes for this by faith and not by the law.
He had shown that faith is necessary, that it is older than circumcision, that it is more mighty than the Law, that it establishes the Law. For if all sinned, it was necessary: if one being uncircumcised was justified, it is older: if the knowledge of sin is by the Law and yet it was without the Law made evident, it is more mighty: if it has testimony borne to it by the Law, and establishes the Law, it is not opposed to it, but friendly and allied to it. Again, he shows upon other grounds too that it was not even possible by the Law to attain to the inheritance, and after having matched it with the circumcision, and gained it the victory, he brings it besides into contrast with the Law in these words, "For if they which are of the Law be heirs, faith is made void." To prevent them anyone from saying that one may have faith and also keep up the Law, he shows this to be impracticable. For he that clings to the Law, as if of saving force, does disparagement to faith's power; and so he says, "faith is made void," that is, there is no need of salvation by grace. For then it cannot show forth its own proper power; "and the promise is made of none effect." This is because the Jew might say, What need have I of faith? If then this held, the things that were promised, would be taken away along with faith. See how in all points he combats with them from the early times and from the Patriarch. For having shown from thence that righteousness and faith went together in the inheritance, he now shows that the promise did likewise. For to prevent the Jew from saying, What matters it to me if Abraham was justified by faith? Paul says, neither can what you are interested with, the promise of the inheritance, come into effect apart from it: which was what scared them most. But what promise is he speaking of? That of his being "the heir of the world," and that in him all should be blessed. And how does he say that this promise is made of none effect?
To prevent anyone from saying that it is possible to have faith and to keep the law at the same time, Paul shows that this is impracticable. For one who clings to the law as if it were of saving force dishonors the power of faith. This is why Paul says that faith is made void, i.e., that there is no need of salvation by grace.… And without faith, there is no promise of inheritance, which is what scared the Jews most of all, because that is what they really wanted. For the promise was that they should be heirs of the entire world.
If only the circumcised are heirs, God has not fulfilled his promise to Abraham that he would be the father of many nations, and it will seem that the nations believed in God without any reason.
[AD 253] Origen of Alexandria on Romans 4:14