Sayid is the key piece, he is Jacob's loophole by yeehalostrox

It seems obvious to me that Jacob is using Sayid's form much like MIB is using Locke's. Look at the poster released before this season depicting the cast at The Last Supper. Sayid is in Judas's spot looking at Locke who is in Christ's spot. This indicates a potential betrayal to the "new king" (if you will) of the island. It is clear after the episode Sunset that Smokey is winning at the moment, and that Jacob's side is up the creek.

Smokey/MIB found his loophole in taking over Locke's form to execute Jacob. Jacob is doing the same, but his is even more of a gamble. John Locke was an easy target, because he was searching for meaning. He had blind faith in Jacob and the Island and was easily persuadable through a series of events to die for the sake of it. (Richard telling him he had to die) The MIB manipulated Locke in a number of ways to get him to die. In this respect it should also I think be said that Ben is also an agent of MIB (or at least was up until Dr. Linus last week) and has been doing his work more often than not.

While Locke was an easy target, Sayid is not. Other than Ben, there is not a single character who comes close to the moral ambiguity of Sayid which is why Jacob chose him. The guy kills and tortures, but at times does so in the name of what may in fact be righteous. He is ambiguous, but Jacob believes--good-- by nature. By choosing Sayid, Jacob is playing his cards close to the chest. MIB would never suspect that Sayid couldn't be on his side after their encounter and Sayid (Jacob) killing Dogen. Even when Sayid (Jacob) says to Ben in Sunrise "not for me"...it is misdirection.

Of course there is a rub, which is why Sayid couldn't kill MIB. I believe that the reason Sayid could not kill MIB is precisely because he is "infected". Jacob believes in Sayid's essentially good nature, even though his soul is black at the moment. Dogen said there is a "scale" in every man. White and Black. From the first season...the title sequence alone. The fact that the title sequence flip flopped at the end of S5 and the Incident. The image of Locke with black and white eyes. There was a changing of the guard at the end of S5. It all adds up.

Sayid is the tipping point because at this point there is still good in him, but it will take time to get it back. MIB will neither suspect Sayid nor will he ever be able to comprehend his free will. He makes false promises built on removing free will and offering false claims. He does not understand free will. He takes the white stone in his cave dwelling and casts it out, not realizing that both are necessary and exist in all of us. He doesn't see gray. Just black and white. I think a major plot point will involve the team Jacob losties figuring out what it means to be "infected" and then getting Sayid fully cured--whatever that means. We still don't know what "infected" means and how it applies to Sayid, Claire, the Dharma members Des watched die, etc-- and what it has meant throughout the entire series. It will be at that point that Sayid will be able to exercise his free will when he is in balance again--and he will kill the MIB.

The entire thing is misdirection on Jacob's behalf. While the circumstances are different here and involve posession and a host of other questions--I am still very much reminded of Harry Potter with Snape and Dumbledore. Snape was DD's agent and ultimate weapon against Voldemort, precisely because he was ambigous and could seem nonthreatening to the other (bad) side. Sayid is the same way. Is he morally corrupt or righteous?

Jacob risk is that he puts all his eggs in the basket of free will. Observe in last week's episode when Miles tells Ben that he (Jacob) was hoping you would make a different choice right up until the last second before you drove th knife in. Jacob never interferes with free will no matter what the potential outcome, even his choices of those who he "picks" he never makes them come to the island. They all have to believe and have "faith" for themeslves. The irony is that even Jack had to have "faith" to return to the island because he had work to do. In Lighthouse, he tells Hurley about Jack that Jack has to see for himself.

In the bigger picture of the entire series, this free will/faith vs. MIB and evil still holds up. The entire conflict on this show has always been based around faith. This whole black/white good/evil dichotomy has been played out since "Man of Science Man of Faith" and arguably even before that in Season 1. It is telling that Potok's "The Chosen" is shown in last week's episode--it is a book about the friendship between two Jewish friends that sees its way through spiritual turmoil, both personal and in the larger societies in which the men live. Apply it to Jacob and MIB (and I think we'll see more of their history in the final episodes) and it works on a personal level and on the island (and beyond) to the larger world.

I went on a tangent, but essentially the entire Jacob/Sayid thing is pure Machiavelli, keep your friends close and your enemies closer. Funny enough, the exceedingly smart writers drop hints as to this too. In the alt timeline last week in Dr. Linus--the principle says to ben "you can execute your Machiavellian schemes"...etc. Lost never ceases to amaze me in the way that it suggests, albeit very subtlely--so much with its dialogue and visual clues. It's not unlike Jacob's touch. It is suggestion and what we do with it is our free will and our thought processes interpreting what we see.

Maybe I'm wrong, but I just have a funny feeling I am right about this.