Abraham is traditionally regarded as the first Jew, but the truth is that he was a "Gentile," the son of an idolater (Josh. 24:2), who heard God's voice and then began his pilgrimage of faith to the land of promise (Heb. 11:8-11).
Moreover, God personally chose Abraham, promising to make him into a blessing, while he was not yet circumcised, and it was only later, after he sacrificed his beloved son Isaac (i.e., the Akedah) that he was promised that in his Seed (זֶרַע) shall all the nations of the earth be blessed (Gen. 22:18). It was the faith of Abraham - especially as demonstrated by the Akedah - that prefigured the justification of the nations through faith.
This is the "Gospel of Moses" which Yeshua alluded (John 5:46). Therefore we read: "And the Scripture, foreseeing (προοράω) that God would justify the nations by faith, proclaimed the gospel beforehand to Abraham, saying, "In you shall all the nations be blessed" (Gal. 3:9).
In other words, God's great plan of salvation was from the beginning for all the nations of the earth to be redeemed....