Regarding Romans 9, this is how my commentary begins,
9:1 — 11:36 The gospel and Israel
Interpreters have often considered these three chapters to have little connection with the real theme of Romans. This section has been understood as an aside motivated by Paul's personal concern for his people, or as a digression on the theme of God's election. But the theme of these chapters is the place of Israel in God's plan of salvation, and this is a theme that is much involved with Paul's concerns in Romans. From the beginning of the letter (1:2; cf. also 3:21, 31; ch. 4)
Paul has been concerned to demonstrate that the gospel stands in continuity with the OT. He wants to make it clear that the coming of Jesus Christ and the new regime of salvation-history that he has inaugurated is no innovation in God's plan for history, but its intended culmination. However, the unbelief of the majority of Jews in Paul's day presents a potential problem for Paul's attempt to establish such continuity. Was not God's promise of salvation given to the people of Israel? How can he remain true to that promise if it is now fulfilled in the church instead of in Israel?
These are the questions Paul answers in chs. 9 - 11, as he defends the thesis that It is not as though God's word had failed (9:6a). Jewish unbelief at the present time does not mean, Paul asserts, that God's promises to his people have failed because
1) God had never promised to save every single Jew (9:6b-29);
2) the Jews are themselves responsible for failing to believe (9:30 - 10:21);
3) God's promises to Israel are even now being fulfilled in a remnant, of Jewish Christians (11:1-10); and
4) God will yet save all Israel (11:12—32). Throughout, Paul is concerned to show that God's promises to his people Israel — when correctly understood - remain fully intact. This 'theology of Israel', in addition to establishing the coherence of the gospel, is also of practical importance. For, as the appeals in 11:12-32 reveal, Paul was aware that the Gentiles in the Roman church were neglecting their indispensable OT 'roots' and looking down on Jews and Jewish Christians.
9:1—6a The issue: Paul's anguish over Israel
The lack of a word or phrase to connect ch. 8 with ch. 9 suggests that there is a pause in Paul's argument at this point. With the celebration of God's unchangeable love for Christians (8:31-39) the climax of his argument to this point has been reached. But it is just this assertion of the certain fulfilment of God's promises to Christians that leads Paul now to raise the question of God's promises to Israel. Vs 1-3 show that this question was an intensely emotional one for him. For Paul never lost his sense of identification with his fellow-Jews. He therefore experiences great sorrow and unceasing anguish over those who are from the standpoint of the flesh (kata sarka) his 'kinsmen' and brothers (2-3).
Although Paul does not tell us why he feels so badly about his fellow-Jews, the parallel in 10:1 makes clear that it is because the great majority of Jews are not saved; for they have refused to believe in Jesus Christ (cf. 9:30 - 10:21). So strongly does Paul feel this, like Moses before him (Ex. 32:31-34), he is willing to sacrifice his own salvation for the sake of the salvation of his fellow-Jews. The strength of Paul's assertion (cf. also v 1) suggests that he may have been aware of some Jews who doubted his concern for his 'kinsmen according to the flesh'.