Home from work early ...
No more white text... if you don't want to be spoiled, you shouldn't be reading this far anyway...
I think that the whole flash-sideways purgatory thing wasn't just purgatory -- it was *Jack's* purgatory - perhaps the whole flash-sideways and church bit was Jack's passage through the "pearly gates" if you're into that sort of thing. It was definitely centered on Jack, and not so much on the others -- everyone else went in the front of the church, Jack in the back, etc.
Christian told us straight up that some of the folks in the church had died before Jack did (duh), but that some died "long after" he did. And yet every single one of them was aged, and was with, the people whom they were closest to at the time of Jack's death, or as Jack would have seen them at that time.
We know (or at least can be pretty certain) that Sawyer, Kate, Claire, Lapidus (the pilot), Miles, and Richard made it off of the island and survived Jack. We know that Hurley and Ben (and likely Rose and Bernard) survived Jack (probably by a long time, in Hurley and Ben's case) on the island. Some of those were in the church, some were not (I didn't notice Lapidus, Miles, or Richard there). But those who survived Jack and were in the church (Hurley, Claire, Kate, Sawyer) were there with those they were close to in Jack's mind... I doubt that Claire, Sawyer, or Kate died alone, for instance. But Claire was with Charlie, Sawyer was with Juliet, and Kate was with Jack himself. Dead people who yet were central in their minds in Jack's eye.
At the very end of the show, the bright light came into the church at basically the same time that we saw Jack's eye close in the bamboo field -- Jack's actual ascent into heaven? We know that the whole church scene was pretty much set outside of time (Christian told us that, too) -- could the entire flash-sideways have taken place in the instant when Jack lost consciousness? Who wants to go to heaven alone? The alternate reality "timeline" got all of the people who were closest to Jack there with him, as happy as they could be (from Jack's perspective, including with those they loved -- providing a reason for the presence of people like Shannon (with Sayid)) when the end came. At the end, Jack and his friends (but not Ben) all go into the light together.
Total speculation, of course. It's just as (if not more) likely the church was simply packed with characters the writers thought the audience liked and could be retained by ABC for the finale. But anyway, that's what the end was, for me -- Jack wasn't my favorite character on the show, but the ending really seemed more about him than anything.