I wonder about this too, and here is my speculation: Before this 144,000 can be united and defined as the 12 tribes of Israel, this verse (Ez. 37:16,17) has to be fulfilled where the ten lost tribes of Israel (the house of Israel) are reunited with the house of Judah or the Jews. Has this happened yet? Ephraim was the head tribe in the house of Israel, the northern territory, and heir to the "firstborn" promise while Judah was blessed by Jacob to carry the sceptre of power as ruler. Jesus came from the tribe of Judah. When the "firstborn" of God fully realizes who it is and unites with Judah who realizes its Messiah, Jesus, then the end can begin where 12,000 from each tribe that are virgins will usher in the coming of the Lord in some way. Of course, I believe that the Church is the lost tribes of Israel as the connection of "firstborn" scriptures throughout the Bible are hard to ignore along with the desription of how these tribes were dispersed into the world and swallowed into the Gentile nations only to come forth as "Sons of the living God".
The stick or rod symbolizes rulership or leadership (Nu.17:2). God promises that there will be one ruler over both houses of Israel one day. And this is why I believe that the Church and the Jews are the two witnesses on earth to the God of Abraham, Isaac, and Jacob. The line of succession is repeated in scripture many times as it shows who the promise of God made to Abraham goes to by inheritance. Ofcourse God never lost anything, especially not His "firsborn" who would receive the covenant promise from God.
Ezekial 37:16 Moreover, thou son of man, take thee one stick, and write upon it, For Judah, and for the children of Israel his companions: then take another stick, and write upon it, For Joseph, the stick of Ephraim, and for all the house of Israel his companions 17 And join them one to another into one stick; and they shall become one in thine hand.
Jeremiah 31:9 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.
Hebrews 12:23 To the general assembly and church of the firstborn, which are written in heaven, and to God the Judge of all, and to the spirits of just men made perfect,
Romans 8:29 For whom he did foreknow, he also did predestinate to be conformed to the image of his Son, that he might be the firstborn among many brethren.
Matthew 15:24 But he answered and said, I am not sent but unto the lost sheep of the house of Israel.
This prophecy was given to the northern territory Israel that was composed of the ten tribes that would come to be the lost sheep of the house of Israel Jesus spoke of and Paul later on pointed out in Romans 9:25,26. Ephraim is the ruler over these ten tribes of the house of Israel, and Joseph his father.
Hosea 1:9 Then said God, Call his name Loammi: for ye are not my people, and I will not be your God. 10 Yet the number of the children of Israel shall be as the sand of the sea, which cannot be measured nor numbered; and it shall come to pass, that in the place where it was said unto them, Ye are not my people, there it shall be said unto them, Ye are the sons of the living God.
Romans 9:25 ¶ As He says also in Hosea: "I will call them My people, who were not My people, And her beloved, who was not beloved." 26 "And it shall come to pass in the place where it was said to them, You are not My people, There they shall be called sons of the living God."
Jer 3:18 In those days the house of Judah will walk with the house of Israel, and they will come together from the land of the north to the land that I gave your fathers as an inheritance.
(Eze 28:25 NASB) 'Thus says the Lord GOD, "When I gather the house of Israel from the peoples among whom they are scattered, and will manifest My holiness in them in the sight of the nations, then they will live in their land which I gave to My servant Jacob.
Jer 31:20 Is Ephraim my dear son? is he a pleasant child? for since I spake against him, I do earnestly remember him still: therefore my bowels are troubled for him; I will surely have mercy upon him, saith the LORD.
