Abraham was a Gentile when God made the covenant of faith with him in Genesis 12-17. He was not circumcised until after the covenant of faith was ratified in the latter half of Genesis 15.
[Gal 3:16 NASB] 16 Now the promises were spoken to Abraham and to his seed. He does not say, "And to seeds," as [referring] to many, but [rather] to one, "And to your seed," that is, Christ.
[Gen 15:5-6 NASB/KJV] 5 And He took him outside and said, "Now look toward the heavens, and count the stars, if you are able to count them." And He said to him, "So shall your seed be." 6 Then he believed in the LORD; and He reckoned it to him as righteousness.
[Gen 17:4-10 NASB/KJV] 4 "As for Me, behold, My covenant is with you, And you will be the father of a multitude of nations. 5 "No longer shall your name be called Abram, But your name shall be Abraham; For I have made you the father of a multitude of nations. 6 "I will make you exceedingly fruitful, and I will make nations of you, and kings will come forth from you. 7 "I will establish My covenant between Me and you and your seed after you throughout their generations for an everlasting covenant, to be God to you and to your seed after you. 8 "I will give to you and to your seed after you, the land of your sojournings, all the land of Canaan, for an everlasting possession; and I will be their God." 9 God said further to Abraham, "Now as for you, you shall keep My covenant, you and your seed after you throughout their generations. 10 "This is My covenant, which you shall keep, between Me and you and your seed after you: every male among you shall be circumcised.
[Rom 4:9-13, 16-17 NASB/KJV] 9 Is this blessing then on the circumcised, or on the uncircumcised also? For we say, "FAITH WAS CREDITED TO ABRAHAM AS RIGHTEOUSNESS." 10 How then was it credited? While he was circumcised, or uncircumcised? Not while circumcised, but while uncircumcised; 11 and he received the sign of circumcision, a seal of the righteousness of the faith which he had while uncircumcised, so that he might be the father of all who believe without being circumcised, that righteousness might be credited to them, 12 and the father of circumcision to those who not only are of the circumcision, but who also follow in the steps of the faith of our father Abraham which he had while uncircumcised. 13 For the promise to Abraham or to his seed that he would be heir of the world was not through the Law, but through the righteousness of faith. ... 16 For this reason [it is] by faith, in order that [it may be] in accordance with grace, so that the promise will be guaranteed to all the descendants, not only to those who are of the Law, but also to those who are of the faith of Abraham, who is the father of us all, 17 (as it is written, "A FATHER OF MANY NATIONS HAVE I MADE YOU") in the presence of Him whom he believed, [even] God, who gives life to the dead and calls into being that which does not exist.
[Eph 1:13-14 NASB] 13 In Him, you also, after listening to the message of truth, the gospel of your salvation--having also believed, you were sealed in Him with the Holy Spirit of promise, 14 who is given as a pledge of our inheritance, with a view to the redemption of [God's own] possession, to the praise of His glory.
So we see that - from the beginning and held within the Torah itself - salvation by faith alone apart from works and the law is initiated. This covenant of faith was given to Abraham and always meant to be to all the nations (God promises he would be the father of many nations), not just to one nation. This God then immediately promises this eternal covenant will be inherited by his "seed" right after saying that he would be the "father of many nations." This strongly indicates many will be adopted children.
[Isa 54:1 NASB] 1 "Shout for joy, O barren one, you who have borne no [child;] Break forth into joyful shouting and cry aloud, you who have not travailed; For the sons of the desolate one [will be] more numerous Than the sons of the married woman," says the LORD.
We see also that Abraham was made righteous for his faith in the gospel of Jesus Christ (according to Galatians 3:8, 16). Those with the same faith in the gospel of Jesus Christ that Abraham had are considered his children and heirs according to the promise.
Next we see that Abraham was made righteous for his faith while he was an uncircumcised Gentile, and that circumcision was the seal of the righteousness of faith. In Ephesians 1:13-14 we see that the Holy Spirit is now the seal of the righteousness of faith... therefore we can conclude that cicumcision is an Old Testament foreshadow of the indwelling gift of the Holy Spirit.
[Rom 2:28-29 NASB] 28 For he is not a Jew who is one outwardly, nor is circumcision that which is outward in the flesh. 29 But he is a Jew who is one inwardly; and circumcision is that which is of the heart, by the Spirit, not by the letter; and his praise is not from men, but from God.
We can see from the Torah that circumcision of the flesh always had this endgame in mind:
[Deu 30:6 NASB] 6 "Moreover the LORD your God will circumcise your heart and the heart of your descendants, to love the LORD your God with all your heart and with all your soul, so that you may live.
As for the scattering of the Jews from their promised eternal possession this is also Biblical. It is anti-Semitic to consider the Jews themselves cursed... it is important to note that it is not the Jews who were cursed, but the land which was cursed.
[Gal 3:13 NASB] 13 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"--
[Deu 21:23 NASB] 23 his corpse shall not hang all night on the tree, but you shall surely bury him on the same day (for he who is hanged is accursed of God), so that you do not defile your land which the LORD your God gives you as an inheritance.
Remember that at Jesus death the sky turned dark for 3 hours. Jesus was not buried before this eclipse ended, so this brought a great curse on the promised land for 2000 years... therefore, were God's chosen people, the Jews, scattered from it.
Jesus became a curse so that the descendants of Abraham would not. After such a great sacrifice of the Lord of taking the curse on Himself to save His people, it is a shame people still say the Jews were cursed.