Sorry, missed this.
I'll say up front that this is error. If you are trying to do the same thing the legalists and Judaizers are doing by creating a "Spiritual Israel" and this is your point, great. Where is your Scripture?
The New Covenant held the promise of New Birth and the eternal indwelling (which is the source of the New Birth) and this promise from the Garden has been for all families of the earth, not just Israel.
And when men are born again they are no longer Jew or Gentile but they are one man in Christ.
God bless.
You can understand John's specific emphasis on being born again, as inextricably linked to Israel's relationship with God.
Their father, Abraham, was barren. Naturally, at his ripe old age, he could no longer have children.
God had to supernaturally intervene in his life to enable him to give birth to Issac.
Thru Issac, thru Jacob, thru his 12 sons, the nation literally came into existence.
Exodus 4:22 had a very insightful verse about this
And thou shalt say unto Pharaoh, Thus saith the Lord,
Israel is my son, even my firstborn:
This was reinforced in Jeremiah 31:9
9 They shall come with weeping, and with supplications will I lead them: I will cause them to walk by the rivers of waters in a straight way, wherein they shall not stumble:
for I am a father to Israel, and Ephraim is my firstborn.
God considered Israel his first born son. They literally became a nation when God supernaturally rescued them from Egypt, separating the waters in the ocean until all of them literally cross over the water in dry land.
But as we all know, Israel broke their covenant of Law that was given at Mount Sinai. They killed or ignored all the prophets that God repeatedly sent to them when they were separated into 2 kingdoms and went into captivity under Babylon, and then under Persia.
Jesus used the parable of the tenants, one of my favorite parables to understand his first coming on Earth to Israel, in all 3 synoptic gospels. (Matthew 21:33-46; Mark 12:1-12; Luke 20:9-19) to illustrate this.
When Jesus and the 12 were preaching from Matt-John, they need to repent of rejecting God their Father in the OT, and believe in his Son is their promised King and Messiah, as foretold by their prophets.
God had mercy on them even when they killed his prophets (e.g. 2 Chronicles 24:20-22; Jeremiah 26:20-30; cf. Luke 13:34; Acts 7:52)., and is now sending his very own Son to Israel, to do a final persuasion to Israel to repent and believe in him.
If they do, as Jesus told Nicodemus in John 3, Israel will be born again.
That is why Paul never mentioned the necessity of being born again to us gentiles. That concept is irrelevant to us.