Romans 11:30-32 — For as ye in times past have not believed God, yet have now obtained mercy through their unbelief:
Even so have these also now not believed, that through your mercy they also may obtain mercy.
For God hath concluded them all in unbelief, that He might have mercy upon all.
God's grace is extended to Gentiles because of Israel's unbelief.
Both Jews and Gentiles are incapable of obtaining salvation by their own efforts, but God's grace is offered to both.
concluded = shut up, as in a trap
Only when all human merit is swept aside can God's mercy take effect — Romans 3:20-21 (Therefore by the deeds of the law there shall no flesh be justified in His sight: for by the law is the knowledge of sin. But now the righteousness of God without the law is manifested, being witnessed by the law and the prophets.)
ye (verse 30) — Gentiles as a group
their (verse 30) — Israel as a nation
verse 31 — your mercy — mercy shown to Gentiles
all (verse 32) — Jes and Gentile
Verse 32 falls in line with the two preceding verses in the following way: Verse 30, (a) disobedience (Jew and Gentile), (b) mercy (Gentile); Verse 31 (a) disobedience (Jew), (b) mercy (Jew and Gentile); Verse 32 (a) disobedience (Jew and Gentile), (b) mercy (Jew and Gentile). — W.E. Vine, The Epistle to the Romans, page 173.