I believe that the cabin was the Nemesis/otherman's home (it's black and he seems to like black). jacob found a way of imprisoning the otherman by a ring of ash. The otherman then used the smoke monster to impersonate dead people eg Christian to intice Claire and give Locke orders. Remember, it was Christian who told locke to die so he could get the others to come back to the island. I believe this was part of the otherman's plan so he could use the smoke monster to impersonate a dead locke and get close enough to kill jacob. you will have noticed that Locke didn't kill jacob, i believe this is because he is the smoke monster controlled by the otherman. back to the ring of ash i believe Claire broke the ring and released the otherman.