Is Jacob Really Christian Shepard? Who Are the Rescuers?

It's only the beginning of the season and there seem to be more and more questions and less and less answers. Here are some more theories and questions. POSSIBLE SPOILERS!

Is Jacob really Christian Shepard?

In the first episode of season 4, it seems as though we get our first glimpse of who we assume is Jacob. And to our surprise, even though it is a very quick glimpse, it looks as if Christian Shepard is sitting inside Jacob's hut. So, many are saying Jacob is Christian Shepard, but I'm not so sure I believe that - at least not yet.

Christian Shepard was dead before they crashed on the island. Since this island seems to have some sort of mysterious powers, I guess you could call them, could it be possible that the island can bring people back to life if they died off the island? Jack has seen his dad on the island, but only briefly. But why wouldn't Christian go to find Jack and stay with him? Maybe because their relationship was sour before Christian died, or maybe he had a previous connection with the island, maybe he has all along, and knows he cannot find his son.

I think it is more likely that Jacob is kind of like an island spirit. He seems to be the boss. And at first we couldn't see him, and it didn't look like John Locke could either. Since, Christian Shepard's coffin was found empty on the island, could it be possible that Jacob has taken the body and is using Christian Shepard's body so he can have a human form? - Just another thought.

But, remember in the season finale of season 3 in Jack's flash forward, he mentions that his father is upstairs, and that if he is anymore intoxicated than his father is, they can fire him from the hospital. So, does that mean Christian Shepard is a live? Has he come back to life? Or maybe Jack was just so intoxicated that he was just spitting things out, not really knowing what he was talking about?

How come Hurley could see Jacob's hut and possibly Jacob?