Some by the world do understand, the world of the faithful, or believers dispersed over all the world: and so in effect it is the same which he said before, that Abraham should be the father of all that believe, whether of the circumcision or uncircumeision. Others by the world do understand the land of Canaan, under which also heaven was typically promised and comprehended: see Hebrews 4:3 Hebrews 11:9,10,16. This, by a synecdoche, is put for all the world; and so also Tabor and Hermen are put for the east and west of the whole world, Psalms 89:12. This was promised to Abraham and to his seed, Genesis 12:7, Genesis 15:18. Was not to Abraham, or to his seed, through the law, but through the righteousness of faith; i.e. it was not made to Abraham because he had merited it by keeping the law; but because he had believed God, and obtained the righteousness of faith. In the whole verse is couched an argument for justification by faith without works, which is the apostle's drift; and it may be thus formed: If the promise of inheritance to Abraham and his seed was to be accomplished not by legal obedience, but by the righteousness of faith; then it follows, that we are justified by faith, and not by works; but the promise of inheritance to Abraham and his seed was to be accomplished, not by the law, but by the righteousness of faith.
Related Commentaries of Romans 4:13
Romans 4:13
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.