Like so many, whether you loved it or hated it, you have now experienced LOST; this is undeniable if you are here, reading these theories. What exactly was that experience?
It was everything one could hope for, in many different ways. We met wonderful people, and we connected to them, as we would connect to friends. We became invested in who they were, and what they felt. We spent 6 years with these people, and now they are gone. But let's take a look at how we got to The End, and what clues they gave us throughout the series.
Desmond. He pushed the button to save the world, failing once, he caused a tragedy. To reconcile this, he turned the key and let it all out. In The End, he went to the source and removed the plug, and once again, he let it all out. (Is it electromagnetism? Is it Higgs Bosons? Remember that Darlton gave us an image of a bottle of champagne bubbling over as an image to describe this season, and the Higgs Boson, aka the God Particle, was recently renamed, colloquially, as the Champagne Bottle Boson...) and his famous line seems pretty pointed now... "See you in another life, brother."
Mittelos. An anagram for Lost Time. The Alt/Flash-sideways turned out to be a cosmic waiting room for everyone. The entry point being the moment that Flight 815 hit turbulence. Desmond appears on the plane at roughly that point, where originally he wasn't there. This is somewhen outside the normal flow of time. It was Lost Time, a place for everyone to wait until everyone is ready. 5 minutes or 5 millennium are irrelevant. If you were chosen, when you moved on, you arrived in this place. I abstain from calling it Purgatory. Limbo makes sense, as by definition, it is the place you wait while waiting for redemption. Christian Shepard (as Kate says "really?! Christian Shepard?) as Jesus Christ parallel was a bit over the top, but considering the battle between faith and science, not too far a stretch, but seems to be a bit of a hit you over the head moment.
Hoffs/Drawler. An anagram for Flash Forward. Everything in the ALT was at some unstated time in the future, after everyone had passed on, and as such, while we were lead to believe they were a flash sideways, they weren't directly.
Canton Rainer. An anagram for reincarnation. Most everyone we care about showed up after they died in this other timeline. This one is pretty straight forward.
We were given clues all along, when you go back and look at everything that was presented to us. There are still many questions that are unanswered, and I would love to have the answers to those questions. There are even more questions to now ask. LOST has always left us gasping, questioning and wondering, and that the finale can continue that trend only serves to add to the wonder that is LOST.
Ultimately, in The End, the love you take is equal to the love you make. All you need is love.
I am a Survivor of Flight 815.
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A few unanswered questions:
Why was Hugo nicknamed "Hurley"? :-)
If they were all meeting up in the sideways, would they have gotten there if Jack didn't succeed in killing Locke/Smokey?
Why couldn't Desmond plug the source once Jack got him back on his feet?