Hi People,
I wanted to wait until I had something to add to the theories, so here it is:
The island grant's immortality, as we have seen in the case of Richard.
The Temple is a place containing the 'elixir' of life, this is how Ben was healed and how Richard never aged. It is quite possible that none of the Other's age. If this is the case, Jack and co might well be hiding out there waiting to play their part in the endgame. 'They're Coming'.
The reason people will go to such lengths to protect or possess the island is because it grants eternal life and the ability to control quantum realities.
I think that the island was discovered in ancient history and has been constantly sought after. I believe they will show that every major civilization, at it's prime, had possession of the island, the Egyptians, the Greeks, the Ancient Romans, the Aztecs and now, Western civilization.
People with immortality can die, but not of natural causes, only if they come to physical harm and even then it can heal.
Jacob has unique access to this 'elixr' and uses it to heal Juliet's sister, for example, or not heal Ben so Jack has to operate on him. He uses this to manipulate events, leading to Locke on the beach using as an example to Ben, of why he should kill Jacob, the fact Jacob let him get sick.
I don't know what the 'elixir' is.
Is it electro-magnetism? Is it a portal to another dimension that exists beyond time and space? Does Jacob skip to the future and the past?
Does Jacob not heal people, but shift them from one quantum reality to another? So for example, he doesn't heal Juliet's sister, he simply shifts a quantum reality into the one Juliet is experiencing, the one where she miraculously recovers rather than the worst case scenario.
Hurley's 'gift' is to be able to communicate with people in these quantum realities, much like Miles. Hurley can communicate with people in other Quantum realities, Miles can hear them and Walt visits them in his dreams.
The 'Man in Black' is trying to stop Jacob from toying with this 'elixir' and using it to manipulate events. Perhaps Jacob has been abusing the power. The Man in Black is a guardian of the 'elixir', seeking to stop Jacob manipulating quantum realities for his own ends, so that fate can play out fully and reach it's natural conclusions. I think the island is the one place quantum reality cannot be manipulated, what happens there actually happens. But beyond the island, I believe it can, so Jacob has to bring people to the island through manipulation in order to maintain control of it. The Man in Black just wants to stop Jacob bringing people to the island to suffer in his miserable games.
'It only ends once, everything before that is progress.' I think Jacob is the one looking to end things and sees all of the destruction and death he wreaks through his manipulation as 'progress' towards his ultimate goal, the 'Man In Black' wants to stop this and just keep the island safe so it's powers cannot be abused by someone like Jacob, or worse. Didn't Einstein say 'Doing the same thing over and over again and expecting different results' was the definition of insanity. I think that Jacob's idea of 'progress' is probably quite sinister and callous and that the ultimate outcome of it can only be bad as it 'ends once'. I don't think the 'Man In Black'is seeking the end of anything but Jacob's game, I think he is trying to 'save the world'. Jacob is the one focussed on progress towards an end, he is certainly the one playing games. What he calls progress will to us appear to be something terrible.
I believe season six will show our favourite characters in the alternate reality of 815 landing at LAX and over the course of the series we will see that in this alternate reality events will transpire that bring them all back to the island by a different route. I think that we will see the 815ers we have been following for the last 5 seasons all die on the island. And I think that when their alt reality selves end up on the island, a scene we might well see is alt Jack and Kate finding their own corpses in the caves. And it all plays out again, Jughead is still on the island, Jack still detonates it but whatever happens, they always end up back on the island ultimately.
We will find out that the island is a place where quantum realities can converge. 'Everything That Rises Must Converge'.
I think by the end we will all be rooting for the Man In Black/Flocke to stop Jacob's manipulations, only for the tragedy of Jacob winning and our friends on 815 suffering for him all over again. And we will be left wondering if the Losties will ever break the loop.