Second, there is nothing in the text to indicate God intended the promise to apply to Abraham’s physical descendants unconditionally, or in perpetuity.

Third, in the New Testament we are told explicitly that the promises were fulfilled in Jesus Christ and in those who acknowledge Him as their Lord and Savior. God’s blessings come by grace through faith, not by works or race (Ephesians 2:8-9).

The Promise:

“I will make you into a great nation, and I will bless you; I will make your name great, and you will be a blessing. I will bless those who bless you, and whoever curses you I will curse; and all peoples on earth will be blessed through you” (Genesis 12:2-3).

“I will surely bless you and make your descendants as numerous as the stars in the sky and as the sand on the seashore… and through your seed all nations on earth will be blessed…” (Genesis 22:17-18)

The Fulfilment:

“The promises were spoken to Abraham and to his seed. Scripture does not say “and to seeds,” meaning many people, but “and to your seed,” meaning one person, who is Christ… There is neither Jew nor Gentile, neither slave nor free, neither male nor female, for you are all one in Christ Jesus. If you belong to Christ, then you are Abraham’s seed, and heirs according to the promise.” (Galatians 3:16, 28-29)

From “Seven Biblical Answers to Zionist Assumptions” by Stephen Sizer.

Simple racist teaching refuted

I add, the verse in Genesis 12:2 – 3 uses two different identification words, “you” and “great nation”.

Definition in the context of the passage:

“you” = Abraham
“great nation” = Israel

Thus, the promise of “I’ll bless those who bless you and curse those who curse you” clearly applies to ‘Abraham’ (the “you” by definition in this passage) and “not” to the ‘great nation’ (Israel) as it’s just “not” mentioned thus.

End.

P/S:
Abraham inherited such a blessing because he was loyal to God but “not” necessarily all his descendants (thus it would be illogical or racist to claim God blindly applies it to any Israelite as a special/racist right of some sort).