The Island is many different things, one of them being a form of Purgatory (I know, I know, just keep reading), this a little different than most ideas of Purgatory, because the Island can be reached by the living (I.E. The survivors of the crash). The Island will take anybody who cannot let go of their past and are not willing to move on, and it will trap them their as a whisper. The reason the Losties were able to go to the Flash Sideways even though they weren't ready to move one, rather than being stuck on the Island as a whisper, is because the Island created the Flash Sideways and it was a reward for saving the Island from the Smoke Monster. When Christian said, "This is a place that you all made together," He meant that the Losties "created it" when they each played their part in saving the Island.
Secondly the Island is conscious, it has a will. The Island is it's own character, there is some debate as to whether or not the Island had a will or if it was all Jacob, I'm adding this to clear up my opinion on that.
The cork and the spring inside the Heart of The Island has always been their since the beginning of time. Nobody created it, it just is. The corks purpose is to keep balance between light and dark. It is a link between the natural and supernatural. It is the point where the realms of the living and the dead meet. The light and the dark depend on eachother; If the light and the dark were to ever be unbalanced than the two worlds would simply cease to exist. The worlds would be ripped apart, and there would be no life, no death, no chaos, no peace, there wouldn't even be empty space, their literally would be nothing.
When the cork was removed in The End this began to happen, the darkness started to leak into the world of the light and the worlds began collapsing in on themselves, because the balance was lost, the darkness was now greater than the light.
There are two physical manifestations of the Light and the Dark when their should only be one, the Light being the Island, the dark being an unseen force. The two are on opposite ends of the cork. But when the Man In Black was thrown into the Light he part of the darkness escaped which killed him. This evil incarnation is known as the Smoke Monster. The Darkness and the Light are parallel to each other, this means that when the Smoke Monster manifests into a human it becomes the dark side of that person and almost believes it is them. This is shown when in the Mobisode, So It Begins, the Smoke Monster is manifested as Christian and refers to Jack as his son. When he is Yemi in the Cost of Living/? he's the dark side of Yemi. This is why when he is in the forms his motivations are:
Yemi - Get Eko to confess his sins, and if he doesn't, kill him. (The opposite/dark side of what Yemi would do) Locke - Leave the Island (The opposite/Dark Side of What Locke would do) The Man In Black - Kill Jacob and leave the Island (MIB would never kill Jacob, even after killing his fake mother he felt sorry immediately afterward)
When I say their should only be one manifestation I mean the light and dark should be in one form together. This used to be the case, Mother was the light/dark together. But when the light when she died the Light was only in Jacob and the Island, and the darkness was able to be released as it's own entity which merged with the Man In Black.
One last thing, Smoke Monsters can die which is why Smother (Smoke Monster/Mother) could be stabbed and killed even though she was one. The only reason why when the Smoke Monster returned and merged with MIB he couldn't die, was because of how Smother made MIB unable to die. ("What's dead?" - the Boy In Black [Smother touches MIB] "Something you will never have to worry about" - Smother)
--GrinningTurtle 20:20, March 25, 2011 (UTC)