Among the various mysteries of God is Israel’s Salvation can mean saved from something (deliverance) or for something (redemption). Paul preached that salvation comes through the death of Christ on the cross which redeemed sinners from death and for a grace-filled life. More, and that in a way no one would normally expect.
As Paul carries on his discussion in Romans 9-11, it appears most of the time that the Jewish people have forfeited their salvation by refusing to accept the gospel of Christ. But at 11:25 there is a sharp turn in the discourse. Paul speaks of a “A mystery is something secret, hidden and not perceived by ordinary means. In the book of Daniel a significant mystery is revealed through divine revelation (Daniel 2); Paul speaks of a mystery of God in Romans 11 and again in Ephesians 3. In speaking of... More” (the Greek mystērion can also be translated “secret”), a divine secret that is being disclosed through the apostle himself. That mystery has to do with the ultimate salvation of the Jewish people. The way of salvation will not be what one might expect (righteousness through observing the law of Moses), but by God’s own mercy and fidelity to the promises made by God to the patriarchs. All of humanity has been disobedient, not just the people of Israel, and God shall have Mercy is a term used to describe leniency or compassion. God's mercy is frequently referred to or invoked in both the Old and New Testaments. More on all (11:32). Following the disclosure of this mystery, Paul becomes a poet (11:33-36), praising God in a beautiful doxology. It appears that the “sorrow” he expressed in Romans 9:2 has left him.