How do we know that God's true Israel is a spiritual people?

The New Testament elaborates on the nature of God's true Israel, describing them as a spiritual people transformed by the grace of God. Romans 9:6 reminds us that 'they are not all Israel, which are of Israel,' indicating that mere ethnic lineage does not determine one’s standing before God. Instead, true membership in Israel involves a spiritual condition defined by faith, as Paul further clarifies in Romans 2:28-29, stating that 'he is not a Jew which is one outwardly... but he is a Jew which is one inwardly.' This emphasizes that spiritual circumcision of the heart is what constitutes true Israel.

Furthermore, the doctrine of the remnant across both the Old and New Testaments illustrates that God's elect are often a small, chosen group who truly worship Him in spirit and truth. Throughout church history, particularly noted during the Reformation, this reality has reaffirmed that faith in Christ and the work of the Holy Spirit bind God's people together, regardless of their ethnic backgrounds. Such spiritual identification assures us that God's people today remain faithful witnesses of His grace.