I dont know where this theory originated from so if its been told here before or credit is due to anyone, sorry. My cousin told me about this theory and it made sense until the third season when a few comments made by the others seem to disprove it.

The theory is that the island is purgatory...the place between heaven and hell. As the show begins and continues on through the first and second seasons we learn that every character has done something wrong, something that would be looked down upon from a moral stand point. (Claire having a baby out of wedlock, Charlies drug addiction, etc). Although some of the characters pasts dont seem to be as bad as others..they all do have things in there past that they arent proud of or they feel guilt for. The theory also states that the "thing" or "monster" in the jungle is Satan himself and the others are his demons or minons.
However as season two ended and season three began I think that theory changes...all the children are taken, aside from Aaron who Ethan tried to take when Claire was still pregnant with him. Then there is the comment that is made to Kate from one of the others, that she is not on the list because she is flawed..if you look back at it all those who have done wrong have been left or killed by the others or the island. So maybe the purgatory theory isnt to far off, maybe people are being taken because they are good? Those left behind arent good enough to be taken to a better place?