The Light explains the seeming omniscience of Season 1 Locke and how Flight 815 Crashed by Darkhunt

I think I know what the "light" is meant to represent.

Firstly, we know the light is responsible for the electromagnetism and the pockets of energy hidden around the island. This was cleared up when the MiB threw the knife at the well and we discovered it was the same light manipulated in the Orchid for the Frozen Donkey Wheel.

Secondly, we know that Flight 815 crashed because Desmond forgot to push the button and the buildup of electromagnetism caused the plane to crash on the island.

In Season 3, the Cost of Living, Locke asks Eko "What exactly did you see back there? I saw it once, you know." He wasn't referring to the Smoke Monster, he was referring to the discharge after turning the failsafe key, engulfing Desmond, Eko and Locke in the same bright light after the hatch imploded. When Eko asked what Locke saw, he says "a very bright light. It was beautiful." referring to his encounter with the 'eye of the island' in Season 1.

Many people wondered back in Season 1 how Locke spontaneously had all this knowledge about what was going on, depsite the fact he didn't really know anything. When Jack asked Locke "what brought us here, John?" we hear Locke reply "The island." Well, if the source of light is the heart/eye of the island, and that was responsible for the electromagnetism in the hatch, then indeed, the island brought them there. Locke knew that because he encountered the bright light, not the monster, in Walkabout. That's why Locke started his crusade as a Man of Faith. That's why it was such a big deal to open the Hatch in Season 1.

If my theory is correct then Locke was right all along, and now we know why. If you ask me, hate Across the Sea or not, that's a big revelation and something I thought we would never have answered from Season 1.