I don't know if this has already been theorized or not.
In season 1, Jack starts to have visions of his father, Christian. When he finally finds the coffin that he was in, SHA-BAM! He was gone. Christian was dead. But his body that's walking around and having discussions with people, says that he speaks for Jacob.
Now, we see Locke in a coffin. But, now he is alive, weird. WHAT IF he is dead. He is like Christian, speaking for Jacob and all that. Will the 316 survivors find a coffin and find that his body is gone, or is Lock a copy, from Jacob.
The point is, is Christian and Locke the "same" or are they 2 dead guys who woke from the dead and have now been employed by Jacob?
Thoughts, theory's, and/or ideas?