The Island was Jail for the Man In Black by Dave

I was struck by one quote in LA X where the Man in Black said "I want to go home."

Whatever type of entity the man in black is - the devil, old world egyptian god, man - he was stuck on the island. He wanted off the island - diametrically opposed to the way that Locke wanted to stay on the island. This is in keeping with the binary oppositions present throughout lost - light/dark, science/faith, black/white, destiny/choice etcetera etcetera.

In the end, however, this Man in Black wants off the island - he wants to go home - and Jacob, his jailer, was keeping him stuck. What is the nature of the cage? Time loop, something else? I'm not sure.

But I think that the entire existence of the island was for the purpose of capturing and holding the man in black. For a long time, I think that he was stuck in the cabin - held there by the ash circle which he can't cross