In all storytelling, there has to be a central point to the story. It can best be summed up as what is the grand struggle that the character(s) must go through in order to reach a their climax destination.
The issues and themes of LOST need to be boiled down to the general essence. For good or ill, the final season was focused upon the vague struggle between Jacob and MIB. This detour into the island's past did not answer why the survivors were tormented in the first five seasons. But if we peel back the onion skin layers of the island participants, we find that throughout island time, there has always been two sides pitted against each other. Jacob and Smokey, a pair of immortals tied together to the island by some unspeakable bond. The Others, who may or may not have been the remains of prior shipwrecks, candidate arrivals or captive in-breeding. The Others have pushed back after some truces against any other group that have arrived on the island: the military, the Dharma science teams, and each other (with the earliest tension the leadership struggle between Eloise and Widmore).
But what were these struggles all about? The many themes that surround the individual stories may be a clue, but the prize seems to be control of the island. But the one person who does actually control things, Jacob, does not want the job. He wants to be replaced. But he does not want MIB to leave if he leaves. (It is like he wants a clean divorce from the island and the smoke monster, so it won't follow him.) But Jacob's need to leave the island to a candidate seems to be overcomplicated: he had centuries to find someone to take over the reins: from brilliant scientists, to egomaniac cultists, to naive average folk. It would seem anyone who actually knows what the island IS, would be happy to take it as a prize. Unless, of course, the island "prize" is the curse that Jacob himself found himself trapped into forever. He was tricked by Crazy Mom, and now he needed to trick someone else to take his job. Perhaps the Smoke Monster was angry about change, or wanted to succeed Jacob as the man/thing in charge. It seems to be a moot point because in Season 6 both Jacob and MIB want nothing further to do with the island. So, in that case, there is no conflict between the two that would lead to more bloodshed of human souls.
The Jacob-MIB story has no moral attributes, centric values or even rewards for persons who want to grow, change or become a better human being. It came down to a disillusioned Jack accepting the job after all his friends stood silently as Jacob begged for help before his light was extinguished (which in itself could have been another lie).
So what was the Big Picture Jack had to finish in order for the island to be saved? Destroy MIB. But why? There was no evidence that MIB could actually "harm" the remaining candidates. There was no clear evidence that MIB was going to destroy the Earth if he got off the island (and some suspect he had already left the island to be illusions on the mainland like ghost Christian to Jack at the hospital). Was it as simple as getting rid of two bickering immoral gods from the human realm of existence? Again, Jack did nothing to accomplish the end of their reign.
And if the island was the creator, the engine for all life, death and rebirth, why would Jacob or MIB ever want to leave it, especially in the hands of less intellectual, less advanced, less experienced people like Jack or Hurley? It does not make much sense that if the struggle was for the whole of the universe, the universe wound up being handed over to a mentally challenged chicken fry cook.
