The Claim Game by Drunkskunk

Now that we have some more answers after "The Substitute", we can get an idea of the big picture. MIB and Jacob represent the two sides.

Light vs. Dark
Good vs. Evil
Free Will vs. Fate
Alive vs. Dead/Underworld

I believe MIB needs people to be dead in order to take their bodies. He's been trying to kill our losties multiple times. Christian led Jack off the cliff in "White Rabbit" and Dave tried to convince Hurley to kill himself. He needs these people dead to "recruit" them which is why I think Sayid will be going to the dark side as he's infected. Claire too, unfortunately has been claimed, so I assume she died in the Dharmaville explosion

Jacob on the otherhand needs people alive to claim them as we saw him touch the losties. He needs someone to usurp his position and keep MIB at bay on the island. Smokey wants to get into the real world and will wreak havoc if he succeeds. Obviously he's considered a major threat to all of us.

The rules are yet to be revealed, but both these sides have to follow a code of conduct. Flocke was going to kill Sawyer so he could infect him. I think now it's clear that smokey can inhabit more than one person at a time. He infected all of Rousseau's crew and Claire and Christian were together in the cabin.

The temple probably has a way off the island, the one MIB is looking for. He needs the losties to help him thwart the temple others and get him access. But the losties need to make the decision themselves, maybe that's what the rules are: Not to coerce people but let them do things based on their own free will.

This is a game. Whichever side can claim more people to rally for their cause will be the victor and determine the fate of mankind.