Romans 11:25-27 meaning

Paul does not want the Gentile brethren, to be uninformed of this mystery (v 25). Paul is explaining the future of Israel to the Gentiles so that you will not be wise in your own estimation (v 25). 

The mystery is that a partial hardening has happened to Israel until the fullness of the Gentiles has come in (v 25). There is an interlude that's been placed in history where history no longer centers predominantly with Israel. History now predominantly revolves around Gentiles. This is observable elsewhere in the Bible, such as Daniel's 70 weeks' prophecy (Daniel 9:24-27). 

In Daniel's 70 weeks' prophecy, the angel tells Daniel there have been 70 weeks (of years, so 490 total years) decreed for his people, Israel, and the Messiah is going to be cut off after 69 weeks (of years, or 483 years). In the 70th week (of years), a great tribulation will occur (Matthew 24:15-22), and then the restoration of Israel will happen, and Jesus will take His place as the reigning king on the throne of David (2 Samuel 7:13).

So far as we can tell, we are currently (as of this writing in 2024) between the 69th and the 70th "week," or period of seven years, of Daniel. Daniel's prophetic clock for the Jewish people has been stopped for around two thousand years now. This interlude is the time of the Gentiles. And the Scripture does not tell us how long that will last. 

The main teaching in the Scripture about the 70th "week" is: Always be ready for Christ's return.

During this interlude that is the time of the Gentiles, a partial hardening has happened to Israel until the fullness of the Gentiles has come in (v 25), but Paul declares that all Israel will be saved (v 26). 

The fullness of the Gentiles is the completion of the era that focuses on the history of the Gentiles. This likely overlaps with the period of the Roman era as described in Daniel 2:40-43. It is during the era of "these kings" that God will set up a kingdom "cut out without hands" (Daniel 2:34) that crushes the kingdom of the Gentiles (Daniel 2:44). 

Daniel's 70 weeks' prophecy was made about Israel, and referred directly to all Israel being saved (Daniel 9:24). Paul emphasizes this in verse 26. 

In verse 29, Paul will insist that God does not revoke His promises. There is hope for the Jews, there is a promise from God that He will take away their sins: Just as it is written, "The Deliverer will come from Zion, He will remove ungodliness from Jacob." "This is My covenant with them, when I take away their sins (vv 26-27)." 

Paul introduces these verses with the phrase Just as it is written to indicate that what follows is from the scripture. The references that follow are from the prophet Isaiah (Isaiah 59:20, 21) and Psalm 14:7. They show that God has promised to redeem Israel, and that the promise is from of old. 

The prediction that The Deliverer will come from Zion is fulfilled in Jesus coming to earth as a Jew. Zion is one of the hills upon which Jerusalem is built, and is often used as a metaphor for the entire country. The phrase The Deliverer that will come translates the Hebrew from Psalm 14:7, which says "yeshua" which means "salvation." This is essentially the same as Jesus's name. So this could be translated "Jesus will come from Zion" and take away their sins. 

Jesus died for the sins of the entire world, including Israel (John 3:16, Colossians 2:14). In doing so Jesus inaugurated a new covenant with all who believe (Luke 22:20). The main thing that is new about this new covenant is that God writes His Law upon the heart (Jeremiah 31:33). The Law will be fulfilled by walking in the Spirit (Romans 8:3-4). 

In Acts 28:20, Paul says he is bound in chains for the hope of Israel, and he is referring to Jesus as that hope. Jesus is the hope of Israel, as well as being the hope for all Gentiles. Jesus died for the sins of the world, and verse 27 promises a day when God will take away the sins of Israel.

We are not told the mechanism of how all Israel will be saved. Since the entire book of Romans emphasizes over and over that righteousness comes by faith, from beginning to end (the theme verse of the letter, Romans 1:16-17) this statement must support the theme of living by faith. 

One possibility is suggested from Jesus's explanation of the parable of the wheat and tares in Matthew 13:36-43. Jesus states that the tares are "sons of the evil one" at the "end of the age." These wicked ones are gathered out of the kingdom by the angels and cast into a furnace of fire. Perhaps that is the way all Israel is saved, by first cleansing Israel of "all stumbling blocks" (offenders) against the righteousness of God. And we know from Romans that those who have believed do not offend God, because believers are covered with the blood of Jesus.

However this takes place, we can be assured that there will come a time when all Israel will be saved.