THE END... this is how it makes sense by YABBA

Lets start with the church scene.... gathered there were the dead souls of our losties, each of them needing all of the others to realise that they are not of the living world now and all that is to be put behind them so they can move on in peace.

christian tells jack that some of his friends in the other room died before him some died after, but their time together on the island was the most impotant thing that happened to them and for their souls to truely be at rest they all needed to be together,

why wasnt ben there? because maybe this wasnt his significant group of people he needed to move on with maybe his significant group included some dharma folk or alex.
you get the impression christian had already moved on with his soul at peace (probably with the group of people that affected his own personal life the most) because he leaves the church to let in the light to take them somewhere to be at peace. this would also explain why a few other faces people were suprised not to see at the church wernt there, they had simply moved on within their own important group. kind of like a spiritual constant?

all that happened on the island really happened! we know when charley, jack sun jin etc etc died, im sure there is a whole other story about how kate and sawyer etc got off the island and lived for a while but as christian says 'everyone dies' so what we all thought was the alternate timeline was infact way in the future after the last lostie had died,

why jack was the last to realise he was dead? time has no meaning where they were it all happened that way so they could all stop being lost souls