Therefore not all who are Israel are Israel. It doesn't matter to God if you are an ethnic Jew. What matters to God is if you belong to his Christ, Jesus. Only by been joined to the King of Israel makes you a true Jew. Paul in his argument with Peter in the book of Galatians takes Peter to task, because Peter when he is with Jews distances himself from believing Gentiles. He brings into his argument with Peter, the fact that the gentiles are justified by faith, just as the Jews are. So the question about who are the people of God, and what is the mark of the people of God is dealt with. Some Jews apparently still saw the food laws as the mark of the people of God. But Paul says no!! The mark of the people of God, is that they are joined to Jesus, Gods Christ. They are joined to Him, through faith alone apart from food laws or circumcision. Faith in Jesus Christ is the mark, or the badge which marks out the people of God.

In Romans 11 again we find the redefinition of the people of God. It must be taken note that, it is a Hebrew of Hebrews, a Jew of Jews who by the revelation of God to Him makes the distinction between true Jews and ethnic Jews. He explains how some of the branches have been broken off of the olive tree. And how the gentiles have been grafted into the olive tree. The Israelite branches were broken off, because of unbelief. We gentiles are only grafted in, through faith in Jesus. So now only believers make up the olive tree, whether Jew or gentile. The point is believing Jews and believing Israelites are one. So it is true to say we who are not ethnic Israel, but believe in Jesus as Gods Christ are the Israel of God.

Ephesians2:12
"Remember that you were at that time separated from Christ, alienated from the commonwealth of Israel, and strangers from the covenants of promise, having no hope and without God in the world....vs15-16 that he might create in himself one new man, in place of the two, that He might reconcile us both to God in one body."
Here we gentiles are spoken of as being alienated from the commonwealth of Israel. Also we were strangers to the covenants of promise. But we have been brought near. We are no longer far away from God. That means we are now part of the Israel of God, because we are the people of God. This means that we are no longer strangers to the covenants of promise. We are included in the New covenant and partake of its promises. We to all intense purposes are the Israel of God. Paul carries on to say that God has made out of the two i.e. Jew and Gentile one new man (vs15) That means that Christ reconciles both Jew and gentile to God in One body, through the cross. Paul actually says in vs19 "We are no longer strangers, but fellow citizens, with the saints and members of the household of God. Can there be any argument, that we with believing Jews are the Israel of God.