As for this episode, I don't have a lot of great insight although I enjoyed the idea that Jin was carrying the money that would get him killed if he had delivered. Fortunately for him, what is normally a bad thing, like losing $25,000, actually saved him.
A lot of people predicted that it was going to be Desmond in the submarine and the funny thing is, I don't think I even cared. Sawyer made note of the locked door and I knew something was going to be in there, but I did not even consider what it could be for a second. Meh.
It's also interesting that the show may wind up ending on the Hydra island and not the mainland. Of course, they could come back but it's weird that the Hydra island is becoming so important so late in the game.
We're getting a little more insight into Widmore's plans and it appears that he is there to kill the Locke Monster. It's strange because why is he so antagonistic to Ben earlier in the show. It's like there are three sides to this whole battle. Maybe what the whole thing is that Jacob oversees the island and has the smoke monster to be the security (against his will) to prevent people who want to use the island for the wrong reasons. It may very be that Widmore has a geophysicist to find the pockets of electromagnetism in order to power some device or solve the energy crisis or what have you, but if it's accessed it will actually doom everything.
Maybe when Jacob was talking about the island being a cork to keep in the "evil and malevolence" that will spread its darkness, he is talking about the electromagnetism. A source of such powerful energy could potentially be the source for a great evil. It is temptation and it is a power that maybe people should not have access to. Jacob is not saying that the Smoke Monster is the evil that will infect the world, but rather the power. For the Smoke Monster, it is hell, because he is trapped there forever to protect it.
Jack and Illana's group is wanting to stop the Locke Monster from leaving because the island will be defenseless. I don't think their goal is to destroy the monster.
I am not sure of the reason that Jacob would bring people to the island. That is the mystery at this point. It could be for his own amusement or to test people or for some other reason that is beyond the main objective which is to stop the exploitation of the island.
There is no real theories here except for the idea that maybe in the end, it will be Widmore versus Locke and Jack. I am liking how this show is shaping up and where it's going. There was maybe no big reveals, but it's a steady revelation of what is happening.