It seems that we can assume whatever else they are (Gods, Demigods, spirits, aliens, time-traveling beings, watchers of humanity?) Jacob and Blackshirt are peers. If we assume that they can each exercise the same abilities, then some interesting realizations can be recognized from earlier scenes in the series. One was touched on by poster Sylik a little bit ago - the notion of a White Smoke monster. Expanding on that, this theory posits that Jacob and Blackshirt can each manifest as "smoke" and take the physical form of a human. For the sake of the viewer, Jacob manifests as Light smoke, Blackshirt manifests as Black - Smokey.
I think this then explains the mystery of Christian Shephard's white shoes back in season one. It's the writers' clue to the viewers that this Christian impersonation is Jacob. In Season 1's "The White Rabbit", this white-shoed vision of Christian ultimately leads Jack to the waterfall, allowing Jack to bring his people a much needed resource for their survival. Blackshirt also uses impersonation of characters to influence the pawns, including a dark-shoed version of Christian that instructs Locke in turning the wheel.
Going back to "The White Rabbit", there's is no question that there is whitish smoke in the scenes in which Jack sees white-shoed Christian. It is tricky to see during the scenes of Jack chasing after Christian through the jungle but there are spots when a light smoke is definitely there.
And in Season 4's "Cabin Fever" when Locke enters the cabin to find Christian and Claire... it's difficult to tell in the dark lighting, but I'm pretty sure Christian is still wearing the white shoes. He confirms that John is there because "he was chosen to be" and seems geniunely impressed that John had figured that much out. When John notices Claire she's almost mocking in her laughter when she says "Don't worry, I'm fine... I'm with him". She is certainly not herself; I suggest she is Blackshirt, who is sensing his game coming together, and Christian is Jacob (with his game coming apart?)
And if true, then we might also posit that the real Claire is dead. So far the impersonations have been of people who have died on the island (Alex, Yemi, Claire?), or who were dead and brought to the island (Locke, Christian). Maybe the concern that Richard and some of the Others have shown over the series regarding the treatment of dead bodies is related? For example, in Season 5's "LaFleur" maybe Richard wanted Amy's husband Paul's body for a reason beyond the "justice" he stated to Sawyer?
I think this then explains the mystery of Christian Shephard's white shoes back in season one. It's the writers' clue to the viewers that this Christian impersonation is Jacob. In Season 1's "The White Rabbit", this white-shoed vision of Christian ultimately leads Jack to the waterfall, allowing Jack to bring his people a much needed resource for their survival. Blackshirt also uses impersonation of characters to influence the pawns, including a dark-shoed version of Christian that instructs Locke in turning the wheel.
Going back to "The White Rabbit", there's is no question that there is whitish smoke in the scenes in which Jack sees white-shoed Christian. It is tricky to see during the scenes of Jack chasing after Christian through the jungle but there are spots when a light smoke is definitely there.
And in Season 4's "Cabin Fever" when Locke enters the cabin to find Christian and Claire... it's difficult to tell in the dark lighting, but I'm pretty sure Christian is still wearing the white shoes. He confirms that John is there because "he was chosen to be" and seems geniunely impressed that John had figured that much out. When John notices Claire she's almost mocking in her laughter when she says "Don't worry, I'm fine... I'm with him". She is certainly not herself; I suggest she is Blackshirt, who is sensing his game coming together, and Christian is Jacob (with his game coming apart?)
And if true, then we might also posit that the real Claire is dead. So far the impersonations have been of people who have died on the island (Alex, Yemi, Claire?), or who were dead and brought to the island (Locke, Christian). Maybe the concern that Richard and some of the Others have shown over the series regarding the treatment of dead bodies is related? For example, in Season 5's "LaFleur" maybe Richard wanted Amy's husband Paul's body for a reason beyond the "justice" he stated to Sawyer?