Events on the island itself during the series finale felt incredibly arbitrary. Let's go over them below:
- Rose and Bernard pulled Desmond out of the well, only for Locke to track them down and threaten to kill the couple unless Desmond cooperated. He agreed.
- On the way to the light source, they ran into Hurley, Sawyer, Kate and Jack. Jack said he was fine with going along with Locke to the light because he'd kill him there. How? He had no real plan, but figured Desmond would be a weapon.
- At the light cave, Desmond was lowered down and essentially put the light out by uncorking it and having it escape. Up top, it started to storm and the island started to crumble. Locke said he was right, assuming the island would soon sink, but when Jack attacked him, Locke bled. Somehow, this made him human.
- Which came in handy later on: Jack and Locke fought on a cliff, as Locke wanted to climb down and get to his boat and sail away. Kate snuck up from behind and shot Locke. He died just like that. Jack sent Kate and Sawyer to the boat, so they could get over to Hydra Island (picking up Claire on the way) and meet up with an alive Lapidus, Miles and Richard, who were firing up the Ajira plane. Ben and Hurley chose to stay with Jack.
- When they got back to the light cave, Jack said he basically had to sacrifice himself to reignite the light. He appointed Hurley as his successor. When Jack got down to the cave, he hoisted Desmond back up, saving his life and successfully returned the light. Hurley saw Jack was not returning and asked Ben to help him be the new protector.
THE SIDEWAYS WORLD we later learned was a form of purgatory. Here's how we arrived there:
- There were numerous moments (such as Kate helping Claire give birth, Sawyer and Juliet touching hands) in which Sideways characters were enlightened. They knew who they were completely and what they had gone through. But not Jack. He was the final one.
- Kate tracked Jack down at David's concert and led him to a church, where she said everyone else was. In back? His father's coffin. Jack went there, but it was empty. He was greeted by Christian Shepard, who explained to us all what the Sideways world was:
It was a place the characters created (when Jacob touched them, we can safely presume) on the island. They had all died, some as we saw on the island, others many years later. But they had been waiting here for everyone to arrive. The place was created so they would find each other, rely on each other to accept the past, learn from it - and "move on," as Christian said. To where? It was never specified.
But when Jack stepped into the church, all the castaways were there. They hugged each other and sat down as Christian opened the main door, and let the light in. Quick cut back to the island, where Jack staggers around, bleeding. He falls to the ground. Vincent comes over and lies down next to him.
Jack sees a plane flying above, and we get a close up of his eye. It shuts.