What I find interesting is that some books of scripture read as poetry, like in the case of Revelation. While others, like Hebrews read as school textbooks. Revelation grabs the reader as a thought-provoking van Gogh, while Hebrews simply puts the reader to sleep. Just an observation.
1) The previous king, Jesus Christ, died and was put in the tomb. His tenure as a Davidic King in the line of Davidic Kings was over, and the next man in line to that kingship inherits that position. We are talking about here on this earth, in mortality. The next in line would have been the oldest son of Jesus. And since he did not have children, then the assignment of Davidic King goes to the oldest living son of Mary. However, Jesus bypassed the oldest living son by appointing John as Mary's son.
King David had done a similar thing when he chose Solomon. Thus, the presiding king, Jesus, appointed his successor John in an orderly transition of governmental power here upon the earth. And this should be easy to see. Not that you have to believe it, but that it is easy to see. Like two plus two equals four is easy to see, but not necessarily easy to believe.
We are specifically talking about Davidic Kings having the Davidic Covenant at their disposal. Anyone not a Davidic King does not enjoy the Davidic Covenant. Jesus to John transitions the Davidic Covenant in the downline of the Davidic Kings. Jesus held the Davidic Covenant and passed that covenant to John as the next Davidic King. Thus, John, as the Davidic King upon the earth, can and will exercise the Davidic Covenant for the protection of his people during the seven years of tribulation and judgment (Rev. 6:17). This is what the sealing of the 144,000 in Rev. 7:4-8 is all about. They are sealed under the Davidic Covenant to their Davidic King so that they are protected during the destructions here upon the earth. Such is the case in Rev. 9:4 that the 144,000 having the seal of the living God can not be harmed. They are sealed under the Davidic Covenant, and only a Davidic King can do that.
2) It is simply a matter of reading scripture at a level. We are all at different levels. So when I read Revelation, I see the book differently than you do. Both are correct, but at different levels. And there is a level of understanding above mine and perhaps more than one.
John has the assignment. Which he accepted in Rev. 10:8-11. The assignment is for the preservation of the saints upon the earth during the tribulation, and after (Rev. 7:12-17). This preservation involves an army (Rev. 19:17-20) of 144,000 (Rev. 14:1) to harvest the saints of God (Rev. 14:14-16) and destroy the beast (Rev. 14:17-20) in the winepress (Rev. 19:15). This is the 3.5-year tribulation ending with the saints having victory over the beast (Rev. 12:11, Rev. 15:2).
Next comes the 3.5-year judgment. It is here that the 144,000 work as judges discerning who can be gathered and who can not (Rev. 16:2-7). The level that I am reading is not necessarily defined by biblical scholars. But I have worked on the revelation for years and see the book all at once. I see how the subjects in the text flow together in the level that I am at.
For example the four storylines. I only cross-reference between the four storylines and never outside the revelation. That is, I restrict myself to only the revelation. And that is the level that I read.
I see the Davidic King throughout the book. The metaphorical phrase "kings of the earth" is the 144,000 (Rev. 17:2, Rev. 18:3, etc.).
So you are asking me to quote verses at the level you are reading, and I am asking you to read the Revelation at a higher level, and I can show you those verses.
