I say then, Hath God cast away his people? God forbid. For I also am an Israelite, of the seed of Abraham, [of] the tribe of Benjamin.
Note 1 at Ro 11:1: Paul's message of grace and his announcement that Gentiles could become a part of the true Israel of God through the new birth without becoming Jews was a startling revelation. Paul had systematically dealt with objections that a legalistic Jew would have to such a message. Here he answered the criticism that this would mean God has forsaken the Jewish nation.
Basically, Paul was saying that Jews are not excluded, but that they just aren't favored over the Gentiles. He cited himself as an example of a believing Jew and compared the status of Israel to that of the Jewish nation in the days of Elijah. In the same way that there were 7,000 true worshipers of God left in Israel in Elijah's day (1Ki 19:18), so there was a remnant of believing Jews in Paul's day.
The rest of this chapter is Paul's explanation of Israel's current relationship to God during the church era.