The characters present in that final church scene are characters both dead and alive in island time, meaning several characters (including Kate, Sawyer and Claire) went on to live a full life beyond the series finale.
The finale of Lost is the most misunderstood of all time.
The final ever scene of Lost – in aptly titled episode “The End” – is intercut between events on the island and an alternate timeline known as the flash-sideways – scenes that replace the flashbacks and flashforwards for the entire final season.
All season long, viewers see the characters rubbing shoulders with one another in LAX, unaware of events shown in the previous five seasons.