"Jacob" is the island. Ben has made the comment that the island has an affinity for certain kinds of people.

What was it Locke said when he was explaining the game of Backgammon to Walt?

"There are two sides; one light, one dark."

A metaphor for the smoke monster, the island, and Jacob, who represents Ben's dark subconscious guilt).

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charlie98210
"Whoa!" she said. "Cry 'Havoc!' And let loose the dogs of war!"
And, like Banquo's ghost, they just won't go away.