Everyone who knows Christ as Savior are now heirs of Abraham, along with believing Jews.
As Paul revealed in his Epistles, the distinction between Jew and Gentile in the churches only was removed. Jews who accept Christ as Savior are now a part of the Church, will be raptured along with the rest of those who know Christ as Savior, and will not be on earth for the Tribulation, otherwise known as "the time of Jacob's trouble" (Jeremiah 30:7).
And while the covenants God made with Abraham are for the Jewish people only, Christians have been "adopted", so to speak, into being heirs of Abraham along with Jews who have accepted Christ as Savior.
The promises were spoken to Abraham and to his seed. The Scripture does not say "and to seeds," meaning many people, but "and to your seed," meaning one person, who is Christ. (Galatians 3: 15-16)
Beloe are two of the many other passages clarifying this subject:
Not all who are descended from Israel are Israel. Nor because they are his descendants are they all Abraham's children. On the contrary, "It is through Isaac that your offspring will be reckoned." In other words, it is not the natural children who are God's children, but it is the children of the promise who are regarded as Abraham's offspring. (Romans 9:6-8)
A man is not a Jew if he is only one outwardly, nor is circumcision merely outward and physical. No, a man is a Jew if he is one inwardly; and circumcision is circumcision of the heart, by the Spirit, not by the written code. Such a man's praise is not from men, but from God. (Galatians 3:15-16)