The End is the Beginning is the End by Richie 007

My theory is that Desmond is a constant between the 2 realities, and as such controls the destinies of everyone, including Jacob and MIB.

I think the series will end with MIB escaping the island, and the "good guys" (Jack, Hurley etc) all failing and most likely dying in the process.

However at the end of season 5 when they detonated the bomb, Juliet said it had worked. It worked because she knew in the same way that Charlie did at the point of death on the plane, that there is another 'universe' (kind of like another 'chance' i suppose) they created by detonating the bomb, where things can be put right again, thus making the loop exist.

Desmond as the constant between these 2 universes (as he always has been), will get the manifest in the sideways universe, re-unite all the 815 folks and get them all back to the island so it begins again. this is his "role".

In a similar way to the matrix and Neo discovering in that film he is actually the 5th Neo. Eloise knows (like the oracle) that this loop occurs, and she wants the outcome where her son is alive, (which we just saw), which means she has to make sure they are all put back on the plane like she did in season 5, thus ensuring they detonate the bomb. so for this to happen again, desmond must re-unite all the 815 to get them back to the island an thus go thru it all again and detonate the bomb creating the happy timeline etc etc etc.

in the past there has always been a constant, but when that constant dies, they are replaced by another constant. this explains the seemingly endless/ageless battle that takes place between Jacob and MIB.

Jacob says he wants people to do the right thing, without him having to tell them. Until they finally do the right thing the constant must exist, to maintain balance and order. MIB wants to break this balance and order, and prove Jacob wrong. The only way he can do this is to escape the island and stop the constant from re-uniting the "candidates" and beginning it all again.

i hope people can follow this!! it's very hard to write it down clearly from my head!!