Ok, something just hit me on the way to work, I'm possibly still just half asleep, but it makes sense to me right now
....
Is it possible Locke (unknowingly to himself) had to die in order for Jack to believe in the Island and become the leader??
1. Jack's family members seem to be tied to the island:
...Jack's Grandpa seemed to know about the island.
...Christian is either working with/for/against Jacob.
...Claire died and is now a "ghost" with Christian. Could be because of her blood lines.
...Aaron was born on the island and "could" be very important later.
2. Christian told a young Jack "Don't be a leader":
...Possibly because Christian was a former leader of the island
...He knew the sacrifices needed to be made and didn't want his son to go thru that.
...Possibly drunk himself to death knowing it was his only way the get Jack and himself to the island.
3. Christian and Locke were both sacrificed to get Jack to the Island:
...The Island thought Jack seeing Christian would be enough to get Jack to become a man of Faith and believe in the Island.
...Jack seeing Locke dead and possibly "resurrected" on the island for the second time will change his views.
And it seems Jack putting the shoes on Locke had nothing to do with science. It was a little test to see if he would have faith that doing that would help. TheO6 didn't seem to crash anyway, they skipped thru time as the Losties have been doing.