I realize you don't really believe in studying the Old Testament. If you had studied it, though, you would know that Israel was divided into two distinct groups shortly after the death of king Solomon.
There is Israel in general, and there is the Believing remnant out of the rest of Israel.
That right there is two groups.
And both are the issue of Abraham after...he was in Circumcision.
And only the latter of those two physical sons of Abraham, Isaac, and Jacob, is the group that is in Isaac...spiritually.
As Isaac was born of God, they are born of God spiritually...
But Abraham also has another seed - a spiritual one that goes back to before he was in Circumcision.
Those Gentiles who believe God.
This is Abraham when he was still UNcircumcision.
Genesis 15:4 And, behold, the word of the LORD came unto him, saying, This shall not be thine heir; but he that shall come forth out of thine own bowels shall be thine heir. 15:5 And he brought him forth abroad, and said, Look now toward heaven, and tell the stars, if thou be able to number them: and he said unto him, So shall thy seed be. 15:6 And he believed in the LORD; and he counted it to him for righteousness.
That is this...
Romans 4:3 For what saith the scripture? Abraham believed God, and it was counted unto him for righteousness. 4:9 Cometh this blessedness then upon the circumcision only, or upon the uncircumcision also? for we say that faith was reckoned to Abraham for righteousness. 4:10 How was it then reckoned? when he was in circumcision, or in uncircumcision? Not in circumcision, but in uncircumcision.
And then there is Abraham's seed after he was Circumcision...
Genesis 17:1 And when Abram was ninety years old and nine, the LORD appeared to Abram, and said unto him, I am the Almighty God; walk before me, and be thou perfect. 17:2 And I will make my covenant between me and thee, and will multiply thee exceedingly. 17:6 And I will make thee exceeding fruitful, and I will make nations of thee, and kings shall come out of thee. 17:7 And I will establish my covenant between me and thee and thy seed after thee in their generations for an everlasting covenant, to be a God unto thee, and to thy seed after thee. 17:8 And I will give unto thee, and to thy seed after thee, the land wherein thou art a stranger, all the land of Canaan, for an everlasting possession; and I will be their God. 17:9 And God said unto Abraham, Thou shalt keep my covenant therefore, thou, and thy seed after thee in their generations. 17:10 This is my covenant, which ye shall keep, between me and you and thy seed after thee; Every man child among you shall be circumcised. 17:11 And ye shall circumcise the flesh of your foreskin; and it shall be a token of the covenant betwixt me and you. 17:12 And he that is eight days old shall be circumcised among you, every man child in your generations, he that is born in the house, or bought with money of any stranger, which is not of thy seed. 17:13 He that is born in thy house, and he that is bought with thy money, must needs be circumcised: and my covenant shall be in your flesh for an everlasting covenant. 17:14 And the uncircumcised man child whose flesh of his foreskin is not circumcised, that soul shall be cut off from his people; he hath broken my covenant.
Genesis 17:19 And God said, Sarah thy wife shall bear thee a son indeed; and thou shalt call his name Isaac: and I will establish my covenant with him for an everlasting covenant, and with his seed after him.
Romans 4:11 And he received the sign of circumcision, a seal of the righteousness of the faith which he had yet being uncircumcised: that he might be the father of all them that believe, though they be not circumcised; that righteousness might be imputed unto them also: 4:12 And the father of circumcision to them who are not of the circumcision only, but who also walk in the steps of that faith of our father Abraham, which he had being yet uncircumcised. 4:13 For the promise, that he should be the heir of the world, was not to Abraham, or to his seed, through the law, but through the righteousness of faith.
You have two groups of Believers.
The Believing remnant of Israel in Isaac before Israel fell (the Little Flock - the Israel...of God).
At which point they were sealed, and the rest were concluded hardened.
Romans 11:4 But what saith the answer of God unto him? I have reserved to myself seven thousand men, who have not bowed the knee to the image of Baal. 11:5 Even so then at this present time also there is a remnant according to the election of grace. 11:6 And if by grace, then is it no more of works: otherwise grace is no more grace. But if it be of works, then is it no more grace: otherwise work is no more work. 11:7 What then? Israel hath not obtained that which he seeketh for; but the election hath obtained it, and the rest were blinded.
And then you have both formerly lost Jews (spiritual Uncircumcision, Acts 7:51-53; Rom. 2:23-25) and Gentiles (Uncircumcision) this side of unbelieving Israel's fall: the Body of Christ...fellow citizens with the saints (with the Little Flock...the Israel...of God).
Romans 4:16 Therefore it is of faith, that it might be by grace; to the end the promise might be sure to all the seed; not to that only which is of the law, but to that also which is of the faith of Abraham; who is the father of us all,