As Locke and Ben walk through the jungle, Ben asks Locke why he bothers walking if he can turn into smoke. Locke says that the he likes the feel of his feet on the ground because it reminds him that he was human.
They then arrive at the well, where Locke discovers that Sayid didn't kill Desmond and someone helped him out with a rope. Locke says that whoever helped Desmond out actually helped him because Widmore said that the Desmond was a fail-safe for Jacob to ensure that Locke never left the island, just in case Locke managed to kill all of the candidates.
Locke then reveals that he plans to use Desmond to do what he can't, which is destroy the island.
And this is where we're left headed into the finale. Jack is the protector of the island and Locke wants to destroy it, so a showdown is coming. More later.