The show repeatedly hammers home the idea that peoples' belief systems are created by their relationship to their parents.
Jack is compelled to fix things through sheer force of personal agency because his father told him he doesn't "have what it takes". Locke desperately needs to believe he has a destiny because he craves a cosmic father figure after his own scammed him out of a kidney. Both fathers are conmen, even if Christian Shepherd had the ostensibly noble motive of giving his son the drive to succeed. Like the historical John Locke wrote, people are all born as blank slates, with our parents as the authors of our personalities.
As the show wears on it becomes apparent that two godlike figures, Jacob and his brother, are playing a cosmic game, with the castaways as pawns. Through unfathomable rules these beings appear and, like conmen, psychologically manipulate the pieces to get them to act according to some ineffable stratagem. The remote and aloof Jacob pushes people into Jack's path while staying removed and letting Jack figure things out for himself, which is all Jack wanted in a father; the Man in Black, meanwhile, is constantly encouraging Locke to embrace his destiny as a savior and as a messiah, which is all Locke wanted in a father. These cons/games may
seem cruel and callous, and yet the Island's mysterious golden heart appears to be safe and everybody appears to have worked out their psychological issues. So, are Jacob and the Man in Black ultimately good, evil, or merely mortal men with godlike powers playing out a petty sibling rivalry?
The answer is that there is no answer. There are as many individual rubrics and value systems for deciding 'meaning' as there are human beings. The only constant is this world we share, and the actions we undertake.
It is a person's emotional baggage that shapes their view of that world. An ambiguous situation may be
accepted as proof or
rejected as a liesaccording to whatever filtering system is bubbling under a person's conscious mind. The central theme of the show is dealing that baggage, because it makes a person vulnerable and easily deluded by charlatans, shamans, and con men. Something the historical John Locke also had quite a bit to say about.
The show's ambiguity is meant for the audience just as much as it is the characters. Recall the final scene, where Jack reconciles with his father under a stained glass window with different religious symbols all radiating out from a central, archetypal light. Just like
The Hero with a Thousand Faces speaks of the world-soul and the navel of the universe in vague terms to encompass all the different cultural variations on the archetype, the show dresses up its archetypal story of conflict between fathers and sons, heroes and gods, and free will versus destiny with allusions to mythology, religion, and popular fiction.
By not limiting the story to a set "answer", it frees the story to become anything and everything a viewer can see in it, like a Rohrschach test [Spoiler\]