I pretty much waited till after LOST was over to start watching it. Right now my wife and I are near the end of the second season. But I have read a couple spoilers, especially Witherington's, so I have a little sense of what's really going on. If you want to watch the series sometime without knowing, then you should stop reading this post now.
I don't know much, except that they're all dead. Fairly often, one of them will say something that's a double entendre in that light. In the last episode I watched, they have a guy they suspect is one of the "others," whoever they are (I know my lack of knowledge will be painful to the faithful). Sahid has tortured him. Anna what's her name has used her police interrogation skills. At the prospect of them keeping torturing him until they know whether they can believe him or until they kill him, he indicates that they will never find enough reason to believe him and says, "I'm dead already."
Last night I was teaching Biblical Interpretation in Indy, and this line struck me as a good way to communicate the notion of "sensus plenior" to the students, the idea that God implanted hidden meaning in the words of the Old Testament prophets that the prophets themselves did not know but that would leap out to New Testament authors who had seen the rest of the storyline.
The man does not know, presumably, that he is dead. When he says, "I'm dead already," he is speaking to an immediate situation. So Isaiah is speaking to an immediate situation when he tells king Ahaz God wants to give him the sign of a young woman giving birth to a son, probably an heir to the throne, perhaps Hezekiah, whose birth will symbolize "God with us," the fact that God is not going to let the kings to the north defeat him.
But those who have seen the rest of the story hear in these words something else. They hear words about the birth of an heir to the world who will be born of a virgin, a king who will be "God with us" in a much more universal and eternal sense. Isaiah does not know the words will take on this meaning in the light of the rest of the story, but those who know the ending do.
And of course, LOST had writers who knew, just as Christians think of God inspiring the prophets. I've at least started writing a good deal of fiction, the creation of dialog and plot is a kind of mystery. I can imagine that lines like this one were a mysterious mixture of knowing where the plot of LOST was headed and a funny double entendre that jumped out of an author's mind. I bet he or she smiled when they found those words flowing from their fingers, almost as if they were not writing them but were carried away by the characters they had created.
And this is something like what someone means when they speak of divine inspiration that is directive in some way and yet preserves the personality and gifts of the human authors.