What does Romans 11:27 mean?
Paul has stated flatly that when the "fullness" of the Gentiles has come to God through faith in Christ, God will remove the hardness of heart from Israel. At that time, all Israel will be saved. That verse (Romans 11:26) presents a series of challenges in interpretation.Paul then quotes from Isaiah 59:20–21 and Isaiah 27:9 to support this idea. In the previous verse, he adjusted Isaiah's words about the arrival of a Deliverer from Zion, likely referring to the Second Coming of Christ. This Deliver will banish sin and ungodliness from Jacob, meaning Israel (Genesis 32:28). Isaiah writes that this "Redeemer" will come to those Israelites who turn from transgression (Isaiah 59:20).
Now Paul uses phrases from both Isaiah 59:21 and 27:9 to quote God as declaring, or renewing, His covenant with Israel at that time when He removes their sin. In the context of Romans 11, the sin of the Israelites will be removed when they obey the gospel and trust in Christ for their salvation.