[HPLovecraft]

Originally Posted by blankall

Spoiler!

From what I got from it, the losties land on the island. The flash sideways is purgotory where they all wait to meet eachother before entering the after life. The flash sideways occured many years after the main storyline when everyone was already dead. Since this was the most significant moment they all had in their lives and they shared it together, they all have to enter the afterlife together.

Spoiler!

The "flash sideways" didn't happen years after. It was always there since time has no meaning in the world they all created (I believe it was Jack's Dad that mentioned this), and they've always been waiting. You can see a hint to this in Ab Aeterno, the Alpert-centric episode. When Alpert "speaks" to his wife, he says he wants to be with her again, and she says you already are. That isn't the exact quote, but it's close to it.