The image of reversal moves to the earth. After the tumult of war, more dramatically described in the last unit, the earth is quiet. What breaks forth is singing, perhaps singing praises of Jehovah.
Once the poetic lens is upon the earth, it can shift to the land of the dead, and does so to further show the humiliation of the previously powerful. Jehovah is the Lord over both the living and the dead, therefore they stir to meet him at his coming. There are pseudepigrapha that describe the scene in the underworld when Christ comes to tear down the gates of death, but that isn’t the image here.
Here, the point is that the dead kings and their dead thrones ask “art thou also become weak as we are?” The point is that in death they have no power. In Israel’s understanding, the dead are powerless and speak with weak whispers. Thus, they were previously powerful, but are now weak. They think perhaps Jehovah is as they are. Of course, Jehovah has power over them, even in death.