2. Who is a Jew? God answers the question

From Sovereign Grace and the Scope of Election: A Comparative Examination of Attainment Theology and Grace Theology, with Particular Attention to the Question of Whether God's Elect Are Found Among All Nations and Religions

"For he is not a Jew, which is one outwardly; neither is that circumcision, which is outward in the flesh: But he is a Jew, which is one inwardly; and circumcision is that of the heart, in the spirit, and not in the letter; whose praise is not of men, but of God" (Romans 2:28-29). Paul applies it: "For we are the circumcision, which worship God in the spirit, and rejoice in Christ Jesus, and have no confidence in the flesh" (Philippians 3:3), written to a largely Gentile church in Macedonia. And John the Baptist had already cut the root of ancestry-confidence: "think not to say within yourselves, We have Abraham to our father: for I say unto you, that God is able of these stones to raise up children unto Abraham" (Matthew 3:9). Jesus pressed the same blade: "If ye were Abraham's children, ye would do the works of Abraham" (John 8:39). The Revelation twice speaks of "them which say they are Jews, and are not" (Revelation 2:9; 3:9), the title belongs to inward reality, not to genealogy, and certainly not to a secular state whose founding charter is not the covenant of grace.