The reason why Paul wrote Romans 9 is to explain why not all Jews were saved. Paul himself was troubled by this that he wished that if it were possible, that he himself would be condemned to hell for all eternity in exchange for the salvation of his fellow Jews.
Back in the first century, there are many Jews who believed that because God made a covenant promise to Abraham, all Jews are considered elect. Paul explained it is not necessarily Abraham’s physical descendants who are elected to inherit salvation, but rather those who has the faith in God that Abraham has. He used Ishmael and Esau (forefathers of the Ishmaelites and Edomites) as examples of those who despite being a physical descendant of Abraham, are not considered elect.
“The reason why Paul wrote Romans 9 is to explain why not all Jews were saved.”
Ok, but what does Romans 9 say?
“So then it is not of him that willeth, nor of him that runneth, but of God that sheweth mercy.”
“Therefore hath he mercy on whom he will have mercy, and whom he will he hardeneth.”
“What if God, willing to shew his wrath, and to make his power known, endured with much longsuffering the vessels of wrath fitted to destruction:
23 And that he might make known the riches of his glory on the vessels of mercy, which he had afore prepared unto glory,”
He speaks here of His sovereignty in saving people, it says He has mercy or He hardens, He prepared the vessels of mercy afore. . .
This is predestination, this is election, this is God’s revelation of His ways. There are many other verses that speak of this, I already cited Ephesians and there are so many others.
We all must embrace the whole of Scripture, even if it is difficult to understand.