The Gentiles, which followed not, &c.— Righteousness or justification, is to be understood here, as ch. Romans 4:3; Romans 4:5.Genesis 15:6. It is the justification by faith, to which the Apostle from the beginning of the Epistle has been arguing and proving that the believing Gentiles have a right, and which they have attained; but which the unbelieving Jews have not attained, because they sought it not by faith, but by the works of the law, Romans 9:32. Therefore what is meant by attaining to this justification, will be clearly understood, if we consider that the Apostle is here giving the reason why the Jews were cast off from being God's people, and the Gentiles admitted to that privilege. See Locke and Whitby.
Related Commentaries of Romans 9:30
Romans 9:30-31
30 What shall we say then? That the Gentiles, which followed not after righteousness, have attained to righteousness, even the righteousness which is of faith.
31 But Israel, which followed after the law of righteousness, hath not attained to the law of righteousness.