Jesus acknowledged that the Jews were the descendants of Abraham, but that they weren’t the “children of Abraham” or the “children of God” anymore, but the “children of the devil”. Since Abraham is not their father, but the devil is, the promises that God gave to Abraham of those blessing Abrahams children being blessed does not apply to the Jews. They rejected Christ and are the children of the devil and not Abraham.
In John 8:37 Jesus said “I know you are Abraham’s descendants”.
in vs. 38, “If you were Abraham’s children,” said Jesus, “then you would[c] do what Abraham did.”
In vs 42, “If God were your Father, you would love me, for I have come here from God.
In vs 44, “You belong to your father, the devil, and you want to carry out your father’s desires.“
It really is quite simple, in the Old Testament only those who were biologically descended could be the “COA”. They had specific blessings and covenants given to their biological lines.
Meanwhile, Jesus comes down and paves the way for everybody to be the “COA” with ethnicity not being a prerequisite. All you have to do to be a “COA” is to accept him now.
Lineage doesn’t matter anymore, there is no covenant to any specific group of people anymore.