Jacob is a powerful manipulator who has been trying to pursue some impossible ideal. Initially, Jacob's intent was altruistic, but his actions became imprudent. Jacob's judgment has been polluted by his adamancy, and he ended up spending much of his life trying to force a particular outcome.
At some point in time, Jacob discovered (or was taught) that the island has an inexplicable power that, when harnessed, can cause a person to possess superhuman abilities.+ Jacob wanted to show others the power, and hoped for some particular outcome. When he wasn't seeing the result he expected, he became determined to make it happen. Jacob's obsession eventually corrupted him, and he began to abuse his powers by manipulating people and events in order to prove he was right. Over time, Jacob’s doings became completely selfish as he lost sight of his once benevolent dreams. He formed a league of followers by bringing people to the island and tricking them into believing that what they will be doing on the island is of the utmost importance. This group became the cult of “others,” and Jacob created a quasi-religious mythology in order to get them to do his bidding. They have been led to believe that Jacob is sharing a power with them that only he can grant them. In reality, the power comes from the island itself, and Jacob's rules allow him to regulate Others' access to it.
Throughout his time on the island, Jacob remained stubbornly controlling and relentless until something caused him to realize the error of his ways. Shortly after this, Jacob began an attempt to set things back on the right course. However, he knew he would have to become a martyr in order to succeed. While still alive, Jacob gave Hurley the guitar case with the ankh as part of his new plan to infiltrate the temple of Others. Jacob allowed himself to be killed by Ben because he understood that his death was inevitable and necessary.
After being stabbed and burnt, the “ghost” of Jacob that visits Hurley on the island is his redemptive self. In a Trojan Horse move, Jacob gets Sayid into the temple so that his body could be fed the dark water, which is enriched with the “good” force of island. The “claimed” Sayid will be able to help to overcome the misled group that the once-living Jacob built up over the years.
Countering Jacob is the Man in Black, who had been trying to fight a benevolent cause that had some fundamental difference to Jacob's. Recently, however, he has become weary of his objective and is now willing to do whatever it takes to be free of his burden. He will possibly go to the extreme to rid the island of Jacob’s followers, and moreover keep people from even getting to the island.
A war will ensue between Jacob’s minions and those of the resistance. Jacob’s people, the Others, are unlikely to be easily convinced that they were coerced into belonging to a faction of malevolence on behalf of Jacob’s selfishness and abusive exercise of power—some may even relish in the powers that Jacob had revealed to them. The war may likely divide those who were once comrades or friends.
The other reality (the non-crash timeline), is the result of a selfish act of interfering with time merely to avoid a particular chance of coming to the island. Without crashing on the island on September 22, 2004, for instance, the 815ers might have had the opportunity to lead a less demanding life (or perhaps simply an island-free life). Each of these individuals will be faced with the choice of living out that life, or to suffer the self-sacrificing consequences of fulfilling a painful but virtuous destiny involving the island. It is not enough to be guided by guilt, coercion, avoidance, or chance alone. To prevail, one must make certain conscious decisions—as tough as those decisions may be.
+Perhaps only individuals born on the island are able to gain these powers, but it is a rare event for an on-island birth to occur. Therefore, there are very few who have the potential to access that power, and fewer still who are able to actually develop it. Those not born on the island can tap into some the island’s numinous energy, but never to the full extent that island natives can.