More or less an attempt to explain Jacob's bottle analogy.
The island has electromagnetic pockets, which, if opened, can unleash a massive amount of energy that could destroy the planet. When the Dharma initiative build the Swan station, they accidentally hit one of these pockets and had to create a mechanism concerned with containing that energy, or rather releasing it in small harmless bouts. It basically worked like a sort of boiler.
Jacob explained to Ricardo that the island is a "cork" sitting on a "bottle" containing evil, which, if unleashed, will destroy the world. If we use his explanation metaphorically, "evil" or "darkness" could stand for the electromagnetic energy and if for some reason Smokey's escape from the island releases that energy, the planet will be ripped apart.
It's not exactly Battle Of The Egyptian Deities, but it does kind of fit the show's brand of sci-fi, doesn't it?