Why The Gravitonium Wants Coulson Dead
Perhaps the biggest revelation from 'Inside Voices' is that the Gravitonium has some form of consciousness. Though this isn't outright stated in the episode, it is established that the Gravitonium has wants and goals. Creel says, after touching it early on in the episode, that "it's alive." Later on when he's attacking Coulson and seeing visions from the Gravitonium, Creel says it hates Coulson and wants him dead. Presumably, the Gravitonium's consciousness comes from the people it has absorbed.
For much of the episode, the only character viewers know to have been absorbed by the Gravitonium was Dr. Franklin Hall. In season 1, Hall fell into the Gravitonium after a scuffle with Coulson, and it was revealed later on that he was still alive - in a fashion - within the mass. As 'Inside Voices' reveals, however, Hall isn't the only person in the Gravitonium. The final scene flashes back to four years ago and reveals what happened to Ian Quinn: He was also absorbed by the Gravitonium, with the help of Raina. Eerily, Raina tells Quinn, "It wanted you." This indicates the Gravitonium, or perhaps Hall inside it, had chosen Quinn.
Related: All the Gravitonium in the MCU
It's unclear for certain why the Gravitonium seems to have a consciousness, whether it's the result of the people inside it or they were absorbed because of a preexisting consciousness. But we do know that it despises Coulson. The most likely conclusion is that the Gravitonium hates Coulson because of Hall's own feelings toward the agent. Still, it would seem that Quinn's consciousness is also alive and well in the Gravitonium based on Creel's comments about his visions. He says that they - presumably Hall and Quinn - argue, but they both hate Coulson.
In the comics, Hall is a supervillain by the name of Graviton, whose molecules were infused with sub-nuclear graviton particles during an explosion that gave him gravitational powers. It would seem that the Gravitonium is Agents of S.H.I.E.L.D.'s way of adapting the comic book supervillain Graviton. But, of course, Graviton takes human form, whereas the Gravitonium is a shapeless mass in the show. At least, for now. Remember that Hale plans to use Hydra's Particle Infusion Chamber to infuse someone's cells with the Gravitonium. It's unclear what would happen to the consciousness of Hall and Quinn if the Gravitonium is infused in someone else's body - would they be erased? Or would their consciousness be added to that of the person whose body is infused?
Coulson is Key to Saving Earth
As of now, we have a number of pieces to the puzzle about how the Earth is destroyed and how the team can potentially save it. We know Coulson's death is a pivotal moment. We know the Destroyer of Worlds is involved, though who exactly that is remains unclear. We know Gravitonium plays a role, likely because it's infused in the cells of whoever becomes the Destroyer of Worlds.
However, now that we know the Gravitonium has a consciousness thanks to the people trapped inside it, the creation of the Destroyer of Worlds becomes even more complicated. Perhaps it doesn't matter who is chosen to become the Destroyer of Worlds - whether it's Daisy, Ruby or someone else - because their consciousness will be overridden by Hall and Quinn in the Gravitonium.
Still, we don't know how it all fits together, aside from knowing Coulson is key. In 'Inside Voices', Robin says of Coulson, "He can put all the pieces together." As with all her other predictions, Robin is vague about what pieces Coulson can put together, but we do know that he has the most information about how to stop the Earth from being destroyed. He now knows of Hale's plan, about the impending alien invasion she's trying to prevent, as well as everything he learned while in the future.
Perhaps Coulson's death in 'Inside Voices' is an indication the agents have already changed the timeline, and they just need him to put all the pieces together to figure out how to prevent the world's destruction - and how the Destroyer of Worlds and Gravitonium factors in. That seems a little easy, especially with six episodes still left in season 5. But with the season heading toward its end, Agents of S.H.I.E.L.D. will have to wrap up the mystery of the Earth's destruction soon enough.
Agents of S.H.I.E.L.D. season 5 continues with 'The Honeymoon' Friday April 13 at 9pm on ABC.