This common justification is fabricated from Paul’s words found in the third chapter of Galatians. I will quote the oft-misquoted verse, but within its context:
The Scripture, foreseeing that God would justify the Gentiles by faith, preached the gospel beforehand to Abraham, saying, “All the nations will be blessed in you.” So then those who are of faith are blessed with Abraham, the believer.
For as many as are of the works of the law are under a curse; for it is written, “Cursed is everyone who does not abide by all things written in the book of the law, to perform them.” Now that no one is justified by the law before God is evident; for, “The righteous man shall live by faith.” However, the law is not of faith; on the contrary, “He who practices them shall live by them.” Christ redeemed us from the curse of the law, having become a curse for us—for it is written, “Cursed is everyone who hangs on a tree”—in order that in Christ Jesus the blessing of Abraham might come to the Gentiles, so that we would receive the promise of the spirit through faith (Gal. 3:8-14, emphasis added).
The “blessing of Abraham” of which Paul wrote in verse 14 was God’s promise to Abraham to bless all the nations in him (which Paul quoted in verse 8), or more specifically, as Paul explained just a few verses later, in Abraham’s singular seed, Jesus (Gal. 3:16). According to what we just read, Jesus provided that promised blessing to all the nations by being cursed by God, dying for the sins of the world on the cross. So the “blessing of Abraham coming to the Gentiles” is not about God making Gentiles materially wealthy like Abraham, but about God’s promise to Abraham to bless the Gentile nations through his seed—and its fulfillment by Jesus through His death on the cross for them. (Paul’s overriding theme here is that Gentiles can be saved by faith, just like Jews, through faith in Jesus.)