The Incident (S5 finale)
You tell them that in the Lost universe there exists an afterlife for souls to go to. We see these souls in Season 6, working through their problems to “come awake” and transcend consciousness.
My personal theory for the show is that the light at the centre of the island is the same light in the afterlife, so had MIB destroyed the island, all characters would “go to hell”, as Richard’s wife tells Hurley.
Lost js the story of a group of survivors quested with the task of ultimately preserving human consciousness, so that souls can move forward and into pure light/consciousness.