But that's not what the New Testament teaches.
It says that all--Jew and Gentile--are called to repent and believe in God's ultimate self-disclosure, the Messiah, Jesus and all be part of God's one people. Joseph L. Mangina gets at this in his very fine commentary on Revelation 7:
It is the unanimous witness of the New Testament that the church is Israel (e.g., Galatians 6:16; 1 Corinthians 10; Ephesians 2:12, 19; 3:6; 1 Peter 2:9-10), the same elected and beloved people of God who were delivered from Egypt, though now under the conditions of the messianic age and with the addition of the Gentiles to Abraham's children after the flesh.Read all the linked passages above to see the basis of Mangina's argument.
As Paul, a Jew who believed in Jesus Christ as the fulfillment of God's plans for the humanity, as the Messiah, and as God-enfleshed writes, that beginning with Israel's patriarch-founder Abraham, righteousness--that is, a right relationship with God--has always been a matter of faith and not of ethnicity, lineage, or the performance of religious duties:
For the promise that he would inherit the world did not come to Abraham or to his descendants through the law but through the righteousness of faith. If it is the adherents of the law who are to be the heirs, faith is null and the promise void...For this reason it depends on faith, in order that the promise may rest on grace and be guaranteed to all his descendants, not only to the adherents of the law but also to those who the faith of Abraham...in the presence of the God in Whom he believed, Who gives life to the dead and calls into existence the things that do not exist... (Romans 4:13-17)Revelation 7:9-17 is one of the Biblical texts for All Saints' Sunday, coming up this weekend.