Last nights episode immediately reminded me of the Twilight Zone episode entitled "The Howling Man." In that episode, the devil (in the form of an ordinary man) is being held in a castle by an order of monks, specifically held in a cell by a "staff of truth." He can't get out unless someone else lets him out. Of course, a stranger comes to the castle and lets him out, even though he was told by the monks that this "man" was actually the devil.
I see so many parallels between that episode and last nights Lost episode. Clearly MIB is trapped on this island (the staff of truth) to prevent him from unleashing his evil upon the world. The monks unsuccessfully relied on the stranger to believe and understand the danger in letting the man out of the cell, much as Jacob initially relied on people brought to the island making the right choices. The devil relies on deceit to facilitate his release from the cell, much as MIB has in manipulating Richard (through the use of his wife) and utilmately Ben to finally kill Jacob.
For whatever reason, the killing of Jacob did not lift the staff of truth and then simply allow MIB to leave the island. He obviously needs to either recruit the remaining candidates to his side or likely kill them as well. It seems that MIB is also unable to kill the candidates himself and thus needs to set up some kind of final battle between the two sides.
And tgreg99...I'm having a hard time believing that this story is going to have a happy ending. I think a lot of our favorite characters are going to die and I think the whole game is going to be restarted by a new candidate taking over for Jacob.
Here is the link to the Twilight Zone episode summary...
http://en.wikipedia.org/wiki/The_Howling_Man