i dont understand lost?

[Johnny]

I still dont fully understand the tv show lost. can you please eplain these questions to me.. Were they allready dead when they first landed on the Island but did not relise it? Was the island purgatry? what were those future visions if everything turned out ok when the plane landed why did they not just live life normally why did they all go to the church at the end and go to heaven? when jack discovered he was dead by his father how did he die was it the last scene where he tried to protect the light or the plane crash itself? was the bright light god or was jack god because he drank the water? does this mean the black smock was the devil and it was a battle between god and the devil? please explain it to me thank you!!!!