I'm rewatching the series and it's been 2 days since Jughead aired. I'm about halfway through season 2. This scene jumped out at me more than anything else given the new season 5 information. The transcript is from Lostpedia, taken from the episode "What Kate Did." Remember, at the time this aired, we never heard of a temple and we were years away from Richard putting the book of laws in front of 5 year old Locke.
[Locke walks toward the kitchen and finds Eko sitting at the table.]
LOCKE: Hello again.
EKO: Hello. I have something I think you should see. If you don't mind, I will begin at the beginning. Long before Christ the king of Judah was a man named Josiah.
LOCKE: Boy when you say beginning, you mean beginning.
EKO: At that time the temple where the people worshipped was in ruin. And so the people worshipped idols, false gods. And so the kingdom was in disarray. Josiah, since he was a good king, sent his secretary to the treasury and said: "We must rebuild the temple. Give all of the gold to the workers so that this will be done." But when the secretary returned, he had no gold. And when Josiah asked why this was the secretary replied, "We found a book." Do you know this story?
LOCKE: No, I'm afraid I don't.
EKO: What the secretary had found was an ancient book -- the Book of Law. You may know it as the Old Testament. And it was with that ancient book, not with the gold, that Josiah rebuilt the temple. On the other side of the island we found a place much like this, and in this place we found a book. [Eko unwraps the book and pushes it toward Locke] I believe what's inside there will be of great value to you.
[Locke opens the book. A square has been cut out, and inside is a piece of film.]
I just took this at face value at the time, no reason not to, plus it introduces the splice of Swan Station orientation film that Eko brought from the Arrow Station. Now, who wasn't completely excited to see the film and immediately forgot the scene we just saw? This might be foreshadowing to what John's destiny might actually be, if he really has one. I am in the camp (notice my "signature") that John is not special, he is being conned and other than living out what has already been determined, there is no greater purpose for him. But if I'm wrong, this might be the answer.
I know we need to see the temple before we can make any concrete answers, but let's kill some time and discuss Locke's destiny.