In chaps. 9-11 Paul deals with a question that may have arisen in the minds of his Christian Jewish and Gentile readers after reading 8:31-39. If God loves the elect (i.e., His chosen people, Israel) and His promises cannot be thwarted, how can He forget His chosen people and promises made to them in the OT?
Thus, Paul’s purpose of writing chaps. 9-11 is twofold. He seeks to vindicate God for temporarily excluding national Israel from His present plan in with the church, and to curb Gentile arrogance since Israel will be regrafted into God’s plan in the future. Paul’s answer covers God’s dealing with Israel’s past (chap 9:1-29), present (chap 9:30-10:21), and future (chap 11).
One should not understand the central issue in these chapters to be predestination, or even Israel’s justification-salvation (though he covers this as well). This section of Romans is about explaining how the promises of God in the Word have not failed (9:6 a). Although many Jews became believers, the majority did not (vv 1-5). And though God has temporarily set Israel aside, He has not nullified His promises to the nation (v 6 a). In light of the overall theme of Romans, this section explains why Israel is experiencing the wrath of God and what they can do to escape it.