Romans 2:14-15 "For when the Nations (Gentiles), which have not the law, do by nature the things contained in the law, these, having not the law, are a law unto themselves: Which shew the work of the law written in their hearts, their conscience also bearing witness, and their thoughts the mean while accusing or else excusing one another".
Because the above incorrectly translates ethnos as Gentiles, people have the mistaken idea that there are some non-Israelite people with God’s Law written in their hearts. This one should be easy to figure out since one doesn’t even have to go to Jeremiah 31 for the context. It is repeated in Hebrews.
Hebrews 8:8-10 "For finding fault with them, he saith, Behold, the days come, saith the Lord, when I will make a new covenant with the house of Israel and with the house of Judah: Not according to the covenant that I made with their fathers in the day when I took them by the hand to lead them out of the land of Egypt; because they continued not in my covenant, and I regarded them not, saith the Lord. For this is the covenant that I will make with the house of Israel after those days, saith the Lord; I will put my laws into their mind, and write them in their hearts: and I will be to them a God, and they shall be to me a people".
This is the new covenant agreement. The quote even includes a physical example so that it would be more difficult for those who destroy the scripture by spiritualizing it. It was a real, physical people who were led out of Egypt and with whom God made the covenants, both old and new. That is specified that the covenant is made only with those of the the two Houses of Israel.
The new covenant includes the House of Israel and the House of Judah, writing God’s Laws in their hearts. Romans 2 talks about some people that the English text calls Gentiles who have the Law of God written in their hearts. Unless God then has violated His own agreement these people must then be Israelites. This is simple logic. The Law of God is only written in the hearts of Israelites. The Law of God is only given to Israel.
Psalms 147:19-20 He shows his word to Jacob; his statutes and his ordinances to Israel. He has not done this for just any nation. They don’t know his ordinances. Praise Yah!
Therefore these “Nations” (Gentiles) must be Israelites. Remember the Greek word in the text is Nation. The word Gentile was a translation error to protect existing church doctrine.
So then logic requires that we look to see who, for almost two thousand years, has most behaved like they have the Law of God internalized or written in their hearts. When we identify those people, we have found true physical Israel.