Lost is for gays and chicks.

um, thrax why do you think they were in purgatory?

I knew it! They were dead the whole time. They say that souls have to go through a process of "letting go" before they move on.

"um, thrax why do you think they were in purgatory?
"

Can I answer? I'm answering.

All of them lived lives unworthy of ascension into heaven. The crash on the island did in fact happen. Their suspension into purgatory immediately commenced upon their crash and the subsequent experiences till the end determined whether or not they were worthy of ascension. Somehow, whoever designed this "place" determined their worthiness equal to the ability for them to cope with the challenges of the island and their ability to get off. To get off they needed to conquer their individual faults.

The eruption evidenced in the cave signifies hell encompassing the island, and a purgatory's transformation into a gateway into hell. "Getting off the island" only meant getting to heaven, and they were always denied departure due to never completing the necessary requirements for ascension.

The Christain Sheperd, and strong religious symbols in the last episode support this.

"All of them lived lives unworthy of ascension into heaven. The crash on the island did in fact happen. Their suspension into purgatory immediately commenced upon their crash and the subsequent experiences till the end determined whether or not they were worthy of ascension."

This state is half true and let me explain why. You are correct in saying that the crash really did happen. You are incorrect in saying that purgatory immediately started upon crashing. Why? They didn't all die during the crash.

Jack's dad explains in the finale that "Some of these people died before you, some long after you". This is supported explictily (Jack being killed by Ben, Juilet and Sayid blowing up) and also implicitly (Ben and Hurley talking about being 1 and 2 as if it happened in the past). The crash itself did not initiate purgatory.

The island did show all the survivors how their lives were lacking and how each of them were yet to be completed.

"Somehow, whoever designed this "place" determined their worthiness equal to the ability for them to cope with the challenges of the island and their ability to get off. To get off they needed to conquer their individual faults."

Again I would disagree. Many of the islanders conquered their faults but were never granted access off the island, most notably Jin and Sun. Characters like Miles and sawyer and clair who left during the final episode were still flawed and most importantly alive. This again defeats your arguement that the crash on the island created death and purgatory.