But when John saw many of the Pharisees and Sadducees coming to his place of baptism, he said to them, “You brood of vipers, who warned you to flee from the coming wrath? Produce fruit, then, in keeping with repentance. And do not presume to say to yourselves, ‘We have Abraham as our father.’ For I tell you that out of these stones God can raise up children for Abraham. The axe lies ready at the root of the trees, and every tree that does not produce good fruit will be cut down and thrown into the fire. Matthew 3:7-10.
It is not as though God’s word has failed. For not all who are descended from Israel are Israel. Nor because they are Abraham’s descendants are they all his children. On the contrary, “Through Isaac your offspring will be reckoned.” So it is not the children of the flesh who are God’s children, but it is the children of the promise who are regarded as offspring. Romans 9: 6-8