The Lost Lowdown

OK. I have barely an idea as to what the loophole might be, but maybe this can get us thinking.

In 1845, an unknown man, "Jacob's enemy", tells Jacob that he wants to kill him and that one day he will find a loophole and be able to. It seems he finds one in John Locke.

"Jacob's enemy" first encounters Locke in 2004. As Lostpedia suggests, "Jacob's enemy" was most likely the person in the cabin in "The Man Behind the Curtain" who said "Help me" to Locke.

In 2007, the circle of ash surrounding the cable appears to have been broken, suggesting that "Jacob's enemy" had been set free (and that he was in fact the one in the cabin in the first place, whom Ben mistakenly thought was Jacob).

So Locke helped "Jacob's enemy" rather than Jacob, albeit unknowingly. There was probably nothing "special" about Locke except for the fact that he ended up in a unique situation, crashing on the island as a survivor, and involving himself in a series of time loops that were able to retroactively invest his life with special meaning.

But how exactly did Locke provide "Jacob's enemy" with a "loophole" through which to kill Jacob? I guess it depends on what the "rules" are... and who makes them. Maybe Jacob himself created the "loophole" inadvertently when he "saved" Locke after falling out a window (Locke appeared to be dead until Jacob approached him and touched his shoulder; in response, Locke gasps and opens his eyes). I believe Jacob may have "resurrected" Locke, and in so doing, made potentially made himself vulnerable to Locke in a way he could not have imagined.

Of course, none of this explains why Jacob was involved in the lives of the survivors at all, especially if he was aware that one of the consequences (of helping them) would be his own death.

There are certainly more "loopholes" in this theory than anything coherent... but maybe it's a start.

I have a few theories on what the loophole possibly is...

1. Jacob seemed to die pretty easily for an immortal man (or god). Is it possible the loophole isn't finding a way to circumvent a rule against killing Jacob, but finding a way that makes it physically possible for Jacob to die.

2. Jacob told Focke (fake-Locke) that "I see you found your loophole." Could it be that Jacob can only be killed by people who have once been leaders of the others.

3. Locke is the only person on the island that we've seen Jacob save off-island and Locke is the only person we've seen leave the island alive, and return dead. Could either of these been the loophole that enabled "Mr. Loophole" shape shift into Locke's body.

I think #3 is least likely because it doesn't explain why Focke had Ben kill Jacob and not just do it himself. It seems he would have had more joy doing it himself. I also think the "Mr. Loophole" is the smoke monster and could have made himself Locke anytime he wanted to without special circumstances.

I think you may be getting close with #2. We know what happens. Through a series of encounters, Locke (just from faith alone in 1954 when he tells Richard that Jacob sent him, and based on the fact that Richard figures out Locke is time traveling) and Focke, convince Richard that he is the leader of the others, appointed by Jacob. This allows Focke to get an audience with Jacob. That's step 1. He likewise convinces Ben, who technically is still the leader. He needs Ben for two reasons. One, I don't think Focke can be the one to physically kill Jacob, and two, since Ben is technically still the leader, he's able to interact with Jacob. All he needs to do then is manipulate Ben into actually doing it. And I have to say, as great a manipulator as Ben is, Focke plays him like a fiddle. He played Locke likewise, first as Christian and later when he has Richard tell Locke that he has to die.