In order for Jack to complete his transformation into Jacob, he had to undergo 5 tests and ONLY HAS ONE LEFT:
1) THAT HIS REAL HOME IS THE ISLAND
Bad things happen when Jack leaves the Island. This place is his home and always has been. The Island has been calling to him for a lifetime. In Season 6 Jack has finally realized that he shouldn’t leave but more importantly he doesn’t want to leave. Jacob’s very definition of Free Will.
***In Season 3, the boat blew up to try and stop him leaving. In Season 4 he was struck down with his Appendix. The Island gets mad when Jack tries to leave.***
***I wouldn’t be surprised to learn that the boy on the Island is a young Jack.***
2) LOCKE CAN NEVER KILL HIM DIRECTLY
Up until the test of character on the sub, Jack made constant comments that Locke could wipe them all out. But the bomb FORCED him into realizing he cannot be killed by Locke. He understands the rules now. And through him his followers have learnt the same.
*** In the Season 3 finale, Locke points a gun at him and is unable to kill him. Even back then Jacob was telling him something.***
3) THE IMPORTANCE OF PERSONAL SACRIFICE
Jack making a promise to Sun to get her off the Island with Jin and watching them die has FORCED him to realize the level of sacrifice he will need to make to be Jacob. The ulitimate test of "having to let go." Personal sacrifice makes a person more determined to achieve their destiny.
***This is something that “The Candidate” taught Jack in spades.***
4) CANDIDATES ARE THERE TO PROTECT HIM
Nobody is more important than him. As Sayid told him, find Desmond because “you are going to need him” Desmond has always been Jacob’s secret weapon (The Variable). Through Desmond Jack can defeat Locke to protect himself and the Island. So:
a) SAWYER WILL DIE
When Sawyer wakes up to realize his decision to go against Jack cost Jin his life, Sawyer will do anything that Jack tells him to do from now on (which is the reason Sawyer is on the island). By dying it allows his Alt version to live and meet Juliet, probably in the same coffee shop that Desmond has agreed to meet Penny in. Afterall, Juliet said “it worked” and talks of them sharing a coffee.
b) KATE WILL DIE IN THE FINALE
Kate only came back to rescue Clare. Once she has achieved that (reuniting Aaron with his Mother), she will die. Desmond saw Clare get on a helicopter in the future and get rescued. Is this what Kate also sees before dying in the finale?
*JACK’S REMAINING TEST*
5) HAVING SOMEONE TO PROTECT OFF ISLAND
The final step in Jack’s transformation. For Jack to stay on island and give himself up to it forever, there has to be SOMEONE off Island that he wants to protect. If Locke ever got off the Island Jack would lose that person. Simply put:
a) KATE WILL LEAVE THE ISLAND IN THE FINALE, or;
b) ALT JACK AND ON ISLAND JACK SHARE CONSICIOUSNESS FOR ON ISLAND JACK TO REALIZE HIS MUST PROTECT HIS SON OFF ISLAND.
*The greatest sacrifice Jack can make, someone who wants to be a good Father, is staying on Island and never seeing his son again, in order to protect him. This will be Jacob’s final test of Jack’s character