13 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.
Long before Moses ever existed, the Lord appeared to Abraham and said: “Go from your country and your kindred and your father’s house to the land that I will show you. And I will make of you a great nation, and I will bless you and make your name great, so that you will be a blessing. I will bless those who bless you, and him who curses you I will curse; and by you all the families of the earth will be blessed.”
It is clear that the law had not yet been given, neither was there as yet circumcision, when the promise was made to Abraham the believer and to his seed, which is Christ, who would cleanse the sins of all. Therefore Abraham was made heir to the world not by the merit earned from keeping the law but by faith. The heir of the world is the heir of the earth, which he obtained in his children. For Christ is the heir of the nations, as David sings: “I will make the nations your heritage and the ends of the earth your possession.”
Here Paul calls circumcision the law, because every commandment can be regarded as part of the law. Abraham inherited the world, either because in his seed (viz., Christ) all the nations which were given to him by the Father might be blessed or because the nations would sup with him in the kingdom of heaven.
Paul says that the righteous will inherit the world because the ungodly will be thrown out and handed over to punishment on the day of judgment, but the righteous will possess the universe which remains, and will have been renewed, and the good things of heaven and earth will be theirs.
[AD 253] Origen of Alexandria on Romans 4:13