Ok, but if we look at that verse it doesn't state that are to become one humanity (as in no physical/ethnic distinction) but the distinction which Paul declares, at least here, is refering to all being a people of God and not a single people group/ethnically. Remember that 'humanity' is made up of diverse ethnic people groups brother but we are all still one people. However, before God we are two, that group He has chosen (Jews) and those groups (Gentiles) He did not.
Paul shows the seperation of the two groups was not based upon ethnicity but was based upon the people/Jews who had been chosen to be God's people and thus seperated from the Gentiles/world. The seperation was made by God that they, the Jews, would be a people unto God. This was the hostility between them, the emnity if you will. God in Christ removed that boundry and encompasses all of humanity, and in this made of who believe one in Christ Jesus as a people unto God. Therefore since we are one spiritually but diverse ethnically, the promises made to 'ethnic' Israel by God still must be fulfilled though all who are in Christ will share in that fulfillment.
Thus in the mil-reign His people are one in essense but distinct in function, just as God is one God in essense and distinct in three persons.
But, maybe I misunderstood what you meant?
Anyway.. what I was intending to state was that both historic premil and Dispy's agree that Israel as a Nation will be gathered back to Himself and as a Nation receive their true King and be saved. And that in the Mil-reign National Israel will still be a literal nation during this time from which Christ shall rule from and over the other nations of the world, which also will be made up of the redeemed as well.
All dipsy's and premil's agree with you here