I have preached for the last two Sundays on becoming a true Jew. The key text has been Romans 2:29, "But he is a Jew who is one inwardly; and circumcision is that which is of the heart, by the Spirit, not by the letter. . ." I even said, "There is no salvation outside Israel." By that I mean that Ephesians 2:11-19 and Romans 11:17-25 teach that the way Gentiles find God and hope is by becoming "fellow citizens" in the "commonwealth of Israel" and by being grafted into Israel. Another way to put it is that "if you belong to Christ, then you are Abraham's descendants, heirs according to promise," because Christ is "the seed" of Abraham and being in Christ means being his "seed" or his descendants and heirs of his saving promise (Galatians 3:29,16).
Now the question is: Are there pointers to this understanding of Jewishness in the Old Testament? Did the Old Testament itself teach that a Gentile could be a "true Jew," and that a Jew by birth might not be a "true Jew"? Here are some lines for you to trace out.
In Genesis 17:25, Ishmael, Abraham's son, was circumcised, and Abraham pleaded with God that Ishmael might be his heir: "'Oh that Ishmael might live before You!' But God said, 'No, but Sarah your wife will bear you a son, and you shall call his name Isaac; and I will establish My covenant with him for an everlasting covenant for his descendants after him'" (Genesis 17:18-19). This shows that mere descendancy from Abraham is no guarantee of being an heir of the promise (a "true Jew"). Similarly Rebekah gave birth to twins by Isaac, but only one of them, Jacob, not Esau, was the heir of the promise (Genesis 25:23; Romans 9:10-13). Thus "it is not the children of the flesh that are children of God ("true Jews"), but the children of promise are reckoned as seed" (Romans 9:8).
In Leviticus 26:41-42, many Jews are pictured as "uncircumcised in heart." "If their uncircumcised heart becomes humbled so that they then make amends for their iniquity, then I will remember My covenant with Jacob." Thus, even though they are physical Jews, they will not inherit the covenant if they do not change inside, similar to what Paul says in Romans 2:29.
In Deuteronomy 10:16-17, Moses commands the people, "Circumcise your heart, and stiffen your neck no longer. For the LORD your God is the God of gods and the Lord of lords . . . who does not show partiality. . . ." This means that heart-circumcision, not physical, external Jewishness is essential with God. Similarly, Jeremiah 4:4 says, "Circumcise yourselves to the LORD and remove the foreskins of your heart, men of Judah and inhabitants of Jerusalem, or else My wrath will go forth like fire and burn with none to quench it, because of the evil of your deeds." Without inward love to God and trust in God, the same wrath comes on Jews as on Gentiles. Thus, as Paul said in Romans 2:25, without heart-circumcision "your circumcision has become uncircumcision."
Jeremiah 9:25-26 says, "Behold, the days are coming, declares the LORD, that I will punish all who are circumcised and yet uncircumcised - Egypt and Judah, and Edom and the sons of Ammon, and Moab and all those inhabiting the desert who clip the hair on their temples; for all the nations are uncircumcised, and all the house of Israel are uncircumcised of heart." These nations clip hair instead of foreskin. Thus they have a form of "circumcision." Jeremiah, amazingly, puts Israel in the same category as these nations under the wrath of God because the mark of their Jewishness is no more valuable than the clipping of pagan hair, if they are "uncircumcised in heart." Again, as Paul said, "your circumcision has become uncircumcision."
Perhaps this is enough to show that, in Romans 2:25-29, Paul is not reinterpreting the Old Testament. He is drawing out a lesson about true Jewishness that was taught by the law and the prophets. True Jews are not those with external marks of Jewishness, but those with circumcised hearts which love the God of Abraham (Deuteronomy 30:6). Therefore Gentiles with faith in Christ, the seed of Abraham, are the children of Abraham, heirs of the promise (Galatians 3:7,29).
Glad to be supported by the root (Romans 11:18). Shalom,