I figured it out by using the bible
Okay im aloser, and anyone who reads this dont think im nuts, but the finale really hit me and i know its prob cause I'm preggo but I WAS OBSESSED!
They all crashed initially on the island, wich i thnk was 'Good and Evil' of the world, like the heart of the world.
I think thats what jacob and his brother were attempting, one wanted to leave it open but if he did it would have brought the light which was the pureness, out of the island where it was kept safe and into our world would come all of the evil.
Jacob had mentioned that the island was the root of all good and if he was to leave all those they knew would die and be basically misterable because the 'dark smoke' which i think was 'evil' would be there rather than kept at bay on the island. jacob and his brother were basically the keeprs, and it was their job to keep evil at bay... I think its close to adam and eve, where eve was tempted by the apple (In this case the smoke monster was tempted by the light) and now knows of good and evil... which i think was the light/darkness jacob his borther etc
Now for the flas sideways...
I think the flash sideways as christian shepherd put it had 'No time there'. When a character who had been on the island would die, they became part of the flash sideways which was purgatory. They didnt realize it was purgatory until they accomplished their goal of being there which I think was for them to be okay with their lives. For example ben was a part of his daughters life where it ended posively rather than in her death.
Lock had a positive relationship with his father which we know wasnt the case but he had to learn to let go.
Jack was with juliet but never really was so i think they were the one that they had been waiting for. Again, since there is no concept of time in that world, so some of them had been living there for years, some of them for months, days etc.
Until they accepted their lives and they all were reconected they wouldnt be able to remember what they were there for to begin with.
It wasnt our 'time' that we are used to, it was no time, and waiting for jack to realize where he was for them all to go to heaven. In order for them to go home, he had to accept what happened....
Jack couldnt accept it i think and thats why they all continued their lives for so long there. I think thats why I along with many others were confuse...
But christian said 'Many beofore you many after tou died' our concept of time compated with the concept of time in pergatory is different. Like we know that some got off the island but we dont know what happened to their lives, we just know they are all dead now...
Which also goes hand in hand with what jacob had said to them that they were all messed up and 'lost souls' That jacob chose them all because they weer on the path of destruction to begin with so they came to challenge and prove themselves inorder to stop the world from the evil that would be 'unleashed' had people found out about it.
I was even thinking, in the beginning Kate makes a comment where she said 'Christian SHepherd' which would mean biblical terms, God, because Jesus was a shepherd, and Jack was the son of Christian... and Jack suffered and died for the world to allow them to live on- again biblical...
Even the part where Jack gets stabbed by 'Lock' reminded me of the stations of the cross, were the crying woman- kate kisses his face and cleans his face, 'Drink this cup, you are now like me' and at the end, the resurection, where jack came 'Out of the cave' after he had died ... it was odd...
I am still trying to put my two senses into it but thats what I got so far. There was alot of biblical references I had never noticed before though!