First of all, I've been reading a lot of these theories over the past few weeks and have to say some of you people have some great ideas! I apologize if I overlap with anybody but I felt compelled to share this :)
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It all comes down to Ben and Widmore...
Some key points here:
First, I think people are taking for granted the fact that Jacob brought our Lost characters to the island and that this isn't necessarily true. All we know for certain is that Jacob somehow _knew_ they were going to end up on the island (he also somehow _knew_ that Locke was going to be pushed out a window). But the characters themselves are a CLOSED LOOP. Oceanic 815 crashed because Desmond didn't push the button. Plain and simple. The electromagnetism caused the plane to crash. This idea is re-inforced by the fact that the Ajira flight _didn't_ crash. For all we know, the island allowed them to come back in (they were at least within its vacinity during a flash).
The whole travelling through time thing was necessary for the swan accident to happen (and thus the button being built, the people crashing...)... notice how that whole affair ended once the incident (the nuke) had occured and now we've barely even so much as spoken of the Dharma time again.
The MIB/Jacob thing is a SEPARATE thing (series/structure of events?) going on from our "candidates." Jacob could see the future so he knew all the people that he would bring or that would somehow end up on the Island. MIB was obviously looking for a way to kill Jacob for _whatever reason_ (for a long time)... and when the plane crashed, he saw an opportunity.
-Side Point- Most or possibly everything MIB has been saying is a lie. We KNOW that a number of things he's said have been lies (the C4, Claire's name being on the rock wall, etc.). I think he was also lying about appearing as Jack's father (he visited Jack in the hospital off-island... he was on the boat!). I think the "island" is a third entity (along with Jacob and the smoke monster)... it used to visit Locke in his dreams... could the smoke monster ever do that?
There are rules to this island. And there are rules to Jacob and MIB's relationship. There are Also rules to Ben and Widmore's relationship; actually it seems like the _same_ rules.
I think Widmore is going to turn out to be working with MIB. He was banished from the island after all (by Ben no less). He's been saying all along that all he wants is to help or save the island, but like MIB we know for certain he has lied about a lot of things and likes to manipulate people.
Widmore and Ben both know A LOT about the island. It's THEIR island. Ben know about the smoke monster; he know about the donkey wheel; all the Darhma stations; the infertility; everything! Presumably Widmore does as well!
The wildcard in all this is Desmond. But he is definitely important. It was HE who caused the original plane to crash. He has a special link with the island. He could/can see the future. Somehow his connection to the island is going to be important.
I think the most important scene to come in the show is when Ben and Widmore finally meet again. I think a lot of people have been forgetting about how much of a build up the conflict between these two had.
Somehow MIB is going to be dealt with; perhaps Widmore has something up his sleeve... but regardless I think it's going to come down to a situation where the pivotal moment or conflict or resolution specifically involves Ben and Widmore (and Desmond) ... (and the island)
Thanks for reading :)