Can you point out which one you are talking about in John Piper's article above?
Because afaik and also according to John Piper himself, Paul's answer is that God's promises to the descendants of Abraham have not failed, even though many Jews are unbelieving and therefore accursed, because the promises were never made to every physical descendant of Abraham.
"It is not as though the word of God has fallen. For not all who are descended from Israel belong to Israel; and not all are children of Abraham just because they are his descendants; 'but through Isaac shall your descendants be named.' This means that it is not the children of the flesh who are the children of God, but the children of the promise are reckoned as descendants." (Rom 9:6-8)
In
Genesis 17:4 God says, "Behold, my covenant is with you, and you shall be the father of a multitude of nations."
They not the seed of Abraham because, even though they trace their physical descent to him, they do not share his faith and obedience. That's why John the Baptist said to the unrepentant Jews, "Do not say, 'We have Abraham as our father!'" (
Matthew 3:9), and Jesus said to the Jews who rejected him, "If you were Abraham's children, you would do what Abraham did" (
John 8:39). In other words, many Israelites (most Israelites) are not the seed of Abraham which will inherit the promises.