Ok, so I haven't been on Lostpedia since before season 6 started. This is because the US was one episode ahead, and I didn't want to accidentally read a spoiler from the next episode. With LOST going on hiatus in the US, but not in Australia, this means I can finally come back to Lostpedia and share my theories with my fellow fans.
Now that that's out of the way, on with my theory. Also, sorry if this has been brought up before, but, like I said, I haven't been on Lostpedia since before season 6 started.
So, in the episode 'Ab Aeterno', Jacob tries to explain the nature of the Island to Richard. He does this by using a bottle of wine and a cork as a metaphor. Jacob says that the wine represents evil, and the cork represents the Island. But, here is where my theory starts, Jacob never explains what the bottle represents. My theory is that the bottle is supposed to be the MIB and the 'evil' Jacob is talking about is the 'sickness', which has infected both Claire and Sayid. The MIB had been called a 'security system' in the past. What is he securing exactly? The sickness! The MIB just wants to leave the Island, but Jacob says he can't. This is because without a bottle the wine won't be contained. The MIB smashing the bottle at the end of Ab Aeterno is his way of saying, "I'm getting off this Island, and there's nothing you can do to stop me."
Once again, sorry if this has already been discussed before. Anyways, feel free to share your two cents about the bottle of wine, or tear my theory to shreds. Either way. :)