Romans 9:31

“But Israel, which followed after the law of righteousness, etc..] The Israelites, the far greater part of the Jews, who were not called by the grace of God, were all very zealous of the law, called “the law of righteousness”; because the matter of it was righteous, it was so in its own nature; and because perfect obedience to it is righteousness; as also because they sought for righteousness by the deeds of it. They very violently and eagerly pursued after it, they tugged and toiled, and laboured with all their might, as persons in running a race, to get up to the law, and the righteousness of it; and yet Israel, with all the pains and labour taken, hath not attained to the law of…”

“But Israel, which followed--"following" after the law of righteousness, hath not attained--"attained not" unto the law of righteousness--The word "law" is used here, we think, in the same sense as in Rom 7:23, to denote "a principle of action"; that is, "Israel, though sincerely and steadily aiming at acceptance with God, nevertheless missed it."”

“But Israel - The Jews. The apostle does not mean to affirm that none of the Jews had obtained mercy, but that “as a people,” or acting according to the prevalent principles of the nation to work out their own righteousness, they had not obtained it. Which followed after the law of righteousness - The phrase, “the law of righteousness,” means the law of justice, or “the just law.” That Law demands perfect purity; and even its external observance demanded holiness. The Jews supposed that they rendered such obedience to that Law as to constitute “a meritorious” ground of justification. This they had “followed after,” that is, pursued zealously and unremittingly. The reason why they did not…”

“9:31 who tried so hard to get right with God by keeping the law (literally who pursued the law of righteousness): Law of righteousness is an idiom that means “righteousness through the law.””

“followed: Rom 9:30-32, Rom 10:2-4; Gal 3:21; Phi 3:6 hath: Rom 3:20, Rom 4:14, Rom 4:15, Rom 11:7; Gal 3:10, Gal 3:11, Gal 5:3, Gal 5:4; Jam 2:10, Jam 2:11 Romans 9:32”