Question: “God raises up a nation, yet in that nation, according to Romans 9:1-9, not all are true Israel. Please explain.”
Answer: I’m glad you referenced the apostle Paul’s declaration in Roman’s 9:1-9.Through the inspiration of the Spirit of God he unfolds for us some of the most profound insights found in all of Scripture regarding salvation.In his NT epistles he fills in much of the “rest of the story” with regard to God’s plan of redemption . God has always had a plan for all people groups;Jew and Gentile(Eph.2:11-3:7)! Perhaps the most direct and straightforward answer to your question is found in Pauls’s letter to the Galatians in 3:29:
“And if you belong to Christ,then you are Abraham’s offspring,heirs according to promise”
Romans 9 :6 states that not all of the “physical seed “of Abraham will receive the promises of salvation.But rather the “heirs according to the promise(Gal.3:29) These are all those who belong to Christ (Jn.10:27-30).The promise of redemption and blessing is found in Abraham’s seed(Christ).
This blessing(eternal salvation) is spirtual in nature and comes to all who are justified by faith alone in Christ alone just like Abraham !(Gen.15:6;Rom.4:3-11) God still has a plan for His people Israel(see Rom 11:1-36) Rest assured God will be faithful to fulfill His promises to national Israel(Ro.11:25-27)!