Romans 9:30-33 — What shall we say then? That the Gentiles, which followed not after righteousness, have attained to righteousness, even the righteousness which is of faith.
But Israel, which followed after the law of righteousness, hath not attained to the law of righteousness.
Wherefore? Because they sought it not by faith, but as it were by the works of the law. For they stumbled at that stumblingstone;
As it is written, Behold, I lay in Sion a stumblingstone and rock of offence: and whosoever believeth on Him shall not be ashamed.
Quote from Isaiah 8:14 — And He shall be for a sanctuary; but for a stone of stumbling and for a rock of offence to both the houses of Israel, for a gin and for a snare to the inhabitants of Jerusalem. (Israel fears an alliance of her enemies, Egypt and Syria.
And from Isaiah 28:16 — Therefore thus saith the Lord GOD, Behold, I lay in Zion for a foundation a stone, a tried stone, a precious corner stone, a sure foundation: he that believeth shall not make haste. Israel trusted Egypt for her deliverance from the Assyrians instead of relying on God.
Law of righteousness — the principle of pursuing righteousness by keeping a law — thinking righteousness will result from keeping the law. "As it were" — they sought it by works
Stumbling stone — Christ, the Messiah (seen by use of the article "Him.")
Offence = trap, the part where the bait was put. Anything that causes a hindrance or prejudice. That makes people fall, as unbelievers do upon Christ.
Israel stumbled by refusing to trust Christ but continuing to pursue righteousness by works.
But Israel, seeking to obtain the righteousness of the law, did not obtain it. Why? Because they sought it by works rather than by faith (verses 31-32). Mark well, the Apostle does not say that they had failed to obtain righteousness because God had not elected them to salvation, but because they had sought to gain it by works rather than by faith. This is important, appearing as it does, at the close of such a chapter as Romans 9. — The Epistle of Paul to the Romans, by Cornelius R. Stam, page 235.