Well, I believe that since Romans 9, Paul has been talking about the distinction of ethnic Israel and Spiritual Israel, see
Romans 9:6. When we get to Romans 11 he says in the beginning of the chapter, "I say then, has God cast away His people? Certainly not! For I also am an Israelite, of the seed of Abraham,
of the tribe of Benjamin. God has not cast away His people whom He foreknew." (v. 1-2a) So he is saying that he is one of the elect who is an ethnic Israelite and confirms he is talking about the elect Jews in verse 7: "What then? Israel has not obtained what it seeks; but the elect have obtained it, and the rest were blinded." So when Paul says "All Israel will be saved" in verse 26, I believe he is speaking towards Spiritual Israel because I do not think he has left that thought in Romans 9:6. There is argument that he is talking about the elect of Israel, I believe R.C. Sproul held that view.
All that to say, I don't have much to say to verse 25 because I myself am sometimes perplexed and still doing my studying, but we can at least know that there is not two people of God, Gentiles: the church, and Jews: Israel. One thing I heard from Sproul was that there has been time in the past that God has focused on the Jews and then on the Gentiles the shift we could see is in
Acts 13:46, but then you also have Peter who focused his ministry to the Jews during the time of Paul, so I mean I am unsure and will refer to
@dsanch1120 comment.