A collection of writings is just an arbitrary choice. It is in no way a “testament” of anything.
If you think there is a testament in there, give a reference to where.
This is the “New Testament:”
Jeremiah 31:
[31] Behold, the days come, saith the LORD, that I will make a new covenant with the house of Israel, and with the house of Judah:
[32] Not according to the covenant that I made with their fathers in the day that I took them by the hand to bring them out of the land of Egypt; which my covenant they brake, although I was an husband unto them, saith the LORD:
[33] But this shall be the covenant that I will make with the house of Israel; After those days, saith the LORD, I will put my law in their inward parts, and write it in their hearts; and will be their God, and they shall be my people.
[34] And they shall teach no more every man his neighbour, and every man his brother, saying, Know the LORD: for they shall all know me, from the least of them unto the greatest of them, saith the LORD; for I will forgive their iniquity, and I will remember their sin no more.
Note that this new testament is with the House of Israel, and The House of Judah, not with any imaginary "church." .
Your posts remind me of this sort of stuff:
https://www.bing.com/search?q=ten+lost+tribes+of+israel
It may be. I do comment to people in my church that though the church claims there are two kinds of people, the lost and the saved, I think there are three: The lost sheep, the found sheep and the goats. I see it as a waste to share the gospel with goats. However, I don’t know who the goats are.
Just thought I’d mention that I have no contention with you regarding Jeremiah. However, it does not mention his relationship with those outside the house of Israel. Also, Paul mentions breaking off new branches and grafting in new branches not from the original tree. This sounds like what Jesus said in the few verses AFTER 15:24.