Romans 9:6-8 NIV

[6] It is not as though God’s word had failed. For not all who are descended from Israel are Israel. [7] 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.” [8] In other words, it is not the children by physical descent who are God’s children, but it is the children of the promise who are regarded as Abraham’s offspring.