Read Romans 9 & 10
Key Verse: Romans 9:15 “… I will have mercy on whomever I will have mercy, and I will have compassion on whomever I will have compassion.”
Chapters 9, 10, and 11 are some of the most controversial in all of Scripture. Controversial because there is explosive potential in interpreting some of what Paul says rather than all of what Paul says.
For instance: in one place Paul, a Jew himself, says “not all who are descended from Israel are Israel…it is not the natural children who are God’s children, but it is the children of the promise [through Isaac — v.7] who are regarded as Abraham’s offspring” (vss. 6,8). This leads you to think that the “chosen people” factor and the messianic mission of Israel have somehow been nullified (at least in any racial or national terms). But Paul later says, “And so all Israel will be saved” (v.26), and goes on to defend this by quoting Old Testament prophetic passages from Isaiah. This leads you to think that the “chosen people” are still uniquely chosen and that God’s relationship with them is inviolable (“for God’s gifts and His call are irrevocable” v.29). So what’s going on here? Is Paul contradicting himself?
There are so many complexities, themes, and sub-themes involved here that I wish I had twenty or thirty pages to help you grasp the flow of Paul’s argument. But there is an absolutely vital quote from Exodus (33:19) that is pivotal to Paul’s presentation. It’s the key verse (9:15) God is sovereign. He will do what He will do, whether we like it or not. No matter that the human attempt to reason through God’s reasons is muddy. He will save those of Israel He wants to save (some or all — it’s up to Him). He will also save those of the Gentiles He wants to save.
But one point is clear. Any “saving” going on will be through one person only: Jesus Christ of Nazareth, Israel’s Messiah and Savior of the world (11:26,27).