Photo from ABC
The Lost writers seemed to have left the ending open for interpretation, so without further ado, here's my crack at a Lost finale explanation:
Like many other fans, I've always maintained that Lost is about purgatory and it looks like this theory -- well, almost -- held up in the final episode.
But, whereas I thought the island adventure was a sort of purgatory, it turns out that the island was, in fact, real. And, instead, the sideways reality was the holding pattern -- a place where the characters went after they died; a place where they had come to terms with their imperfections and worked out their issues; a place where they could come together with the people who were most important to them before moving on to whatever it is that comes next.
Jack is the best example of this because -- as Jimmy Kimmel said -- this was primarily a story about him. Jack obviously had work-life balance issues, substance abuse issues, god complex issues, daddy issues, and above all, issues with his sense of self. On the island he painfully struggled with these limitations on a daily basis until the end culminated with him ultimately fulfilling his purpose: saving the island (even though it cost him his life).
But in the sideways world Jack was peaceful, confident, purposeful, and -- dare I say -- happy? We're never free of our imperfections and limitations, but in this world, Jack (along with the other characters) seems to have accepted and made the best of his. He works on having a good relationship with his son, he's using his skills as a doctor to help John Locke walk again, he's resolved his conflict with his dad, he's found true love.
(Or, at least, that how it seems to me. Who really knows? If you hate my theory, check out April's takeaway, where Jack is the master caretaker, imagining the perfect world in which they landed at LAX and everything worked out for everyone -- I kinda like it.)
In my mind, the island is equivalent to the test of life; and the sideways reality is the space where you observe and accept the struggles while being able to appreciate the journey and be with the important people you've met along the way.
And, then you move on -- to what exactly? Well, that's a whole other post.
How do you interpret the Lost ending?