True Israel
Romans 9:6-8 makes an important distinction concerning the nation of Israel: “For they are not all Israel, which are of Israel.” Paul is not teaching that God’s promises to Israel somehow failed. Even though much of the nation rejected Christ, the word of God had not taken “none effect.” God had preserved a believing remnant within Israel who received His promises by faith (Rom 3:1-4; Rom 9:27; Rom 11:1-7).
Physical descent alone never guaranteed that someone would inherit those promises. Paul demonstrates this through Abraham’s sons. Both Ishmael and Isaac were Abraham’s physical seed, and both were circumcised, but God specifically said, “In Isaac shall thy seed be called” (Rom 9:7; Gen 17:15-21). Ishmael received a blessing, but God established His covenant through Isaac. As Romans 9:8 explains, “They which are the children of the flesh, these are not the children of God: but the children of the promise are counted for the seed.”
This same principle appears elsewhere in Scripture. Romans 2:28-29 shows that being a true Jew under the law involved more than an outward identity in the flesh; it was a spiritual issue of the heart and faith. Likewise, in John 8:37-47, Jesus acknowledged that the unbelieving Jews were physically Abraham’s seed, yet said they were not truly Abraham’s children because they rejected God’s truth and rejected Christ, and were of their father the devil.
This does not mean that the Body of Christ is “spiritual Israel.” That conclusion and extrapolation from this passage leads to the error commonly called replacement theology. Paul continues to distinguish Israel from the Body of Christ all throughout Romans. Israel is presently fallen and blinded in part, yet still has a prophetic, earthly purpose and a future restoration according to God’s promises and election (Rom 11:11-15, 25-29). The Body of Christ, however, is a new creature in which the former distinction between Jew and Gentile has no spiritual standing before God, and it has a heavenly calling, purpose, and destiny (Gal 6:15-16; Eph 2:14-16, Php 3:20).
While Romans 9 is a popular battleground for various doctrines, the lesson in this passage is simple: heritage never replaces the need for faith. Being born into Israel did not automatically make someone a child of promise, and being born into a Christian family does not save anyone today.
Salvation is personal. Today, we must individually trust the gospel of the grace of God alone, believing that Christ died for our sins, was buried, and rose again. We are saved entirely by grace through faith in that work of Christ, and no works of our own contribute to our salvation in any capacity (1Co 15:1-4; Eph 2:8-9).