Many times the scripture uses the phrase many nations. It has been common to understand that phrase in a general way to include various nations of the world or all of the different nations of the world.
Let me suggest that the context of that phrase has been ignored. Let me suggest that if one carefully checks the Greek and the context that at times that phrase does not represent a general world wide group of all nations.
We are told three times in scripture that Israel would fulfil these prophecies.
Genesis 17:4-6, “As for Me, behold, My covenant is with you, and you shall be a father of many nations. And your name no longer shall be called Abram, but your name shall be Abraham. For I have made you a father of many nations. And I will make you very fruitful, exceedingly. And I will give you for nations. And kings shall come out of you.”
Genesis 35:11 “And God said to him, I am God Almighty; be fruitful and multiply. A nation and a company of nations shall be from you. And kings shall go forth from your loins.”
Genesis 48:19 “And his father refused and said, I know, my son, I know. He also shall be a people, and he shall become great. But his younger brother shall become greater than he, and his seed shall become a multitude of nations.”
In Genesis 48:19 the word translated multitude actually means a fullness of nations. Interesting. Those are all very physical promises. Spiritualizing those verses adds to or changes the original meaning. To do so is another gospel.
With people falsely believing the Jews are Israel, this prophecy has been ignored and forgotten just like the promise of a new promised land outside of the old home of Israel, 2 Samuel 7:10.
My suggestion is that when you see the phrase many nations in the new testament, consider that the many nations are the nations of Israel. Yes, all of the instances of the phrase many nations are consistent with the context and prophecy above.