There was a great emphasis on the main characters "awakening" in the sideways world - - - to remember the "importance" of their island time together - - - in order to "move on" in the after life.
The term "awaken" refers to a process which most fans do not acknowledge as a premise for the show.
To "awake" means to stop sleeping; wake from sleep; or to cause (someone) to wake from sleep. It could also mean to regain consciousness or to become aware of a realization. It can also be to become active again, such as "there were echoes and scents that awoke some memory in me."
However, the adjective of awake means not asleep, i.e. the noise might keep you awake at night.
So what did this mean in the context of LOST?
The most obvious would be that the characters were in a dream state; that they were not awake. If we put that into the situation of the island, that means all the characters and actions were part of a complex dream world. If it was a complex dream world, was it the dream of a single person or a collective network of separate dreamers interacting with each other.
If the latter is true, then how would the main characters be "together" in the dream world. There are a few possibilities:
First, all the characters are together in one place. For example, a medical hospital undergoing various treatments. As they are hooked up to their medical equipment (including life support and computer EKG readings), their subconscious filters through the system and interacts with the other patients who are in a similar dream state.
Or, all the main characters are actually children in an orphanage. This would explain, in part, the deep rooted parental issues, betrayal and abandonment. It would also feed the persistent character trait of personal loneliness. Children in an orphanage would naturally dream intense fantasies because they believe their current lives are dark and lonely.
Second, that the characters are in a coma state - - - either as a result of accidents or as part of grand scientific research experiment. The latter would tie into the Dharma experimentation in mind control and manipulation of unique energy systems. The human brain is the most complex energy system in the planet; and one which most mainstream science still does not fully understand. By containing the brains of diverse individuals in a deep control group (such as in a coma state), the researchers could feed their minds with various scenarios to see how they react. For example, inject the terror of a mysterious smoke monster into their minds to see how they would process that information in their patient's dreams.
Third, that the characters were actually "awake" but in a virtual reality that was the island. This could also be an experiment on how the brain works in regard to virtual soldier technology. We know that the defense department and government agencies have used virtual reality systems to train soldiers for combat missions. This would be a leap forward in technology, almost Avatar like, dealing with missions in real time. Perhaps in the future, as referenced in an old Star Trek episode, wars would be fought by soldiers in a virtual reality setting, to avoid the human pain and suffering of real warfare.
But if the characters were participants in this virtual combat world, why would they not "remember" it. If the technology was sufficient to implant the game program into their minds, it probably would have been just as easy as to erase or block those memories once the characters were no longer needed in the experiment.
So the concept of awakening in the series had to mean that the characters woke up or remembered something critical in their past (i.e. the island). After losing their conscious to a virtual dream world called the island, the characters were put back into normal situations to live normal lives as shown in the sideways world. Now this would work perfectly as a reasonable explanation of the entire series except for one critical plot detail. In the sideways world, everyone was dead.
This gets us back to the last definition of the word: to become aware of a realization.
I have thought for a long time that knowledge is power. If one knew what was going on at any moment in time, they could control their own destiny. Early on, I thought that Rose became fully aware of what the island really was because the pain of her incurable cancer was gone after the plane crash. Rose became aware on the beach that she had died in the plane crash. That is why she thought everything would be alright; that she would meet up with her husband soon.
This is also why Rose and Bernard later broke away from the survivors and their dramas with the island inhabitants. They knew that what they were up to was not "real." Rose and Bernard wanted to keep to themselves so they could enjoy the "extended time" they were granted, together.
It would also explain why we did not see Rose and Bernard "awaken" in the sideways world. They did not have to awaken. They already knew of their deaths while on the island. It would seem that all the LOST souls had to awaken by themselves - - - and once each individual came to the realization that they were actually dead, could their souls move on in the after life (as depicted at the ending of the sideways church scenes).
Everything up to that point was the individual's subconscious not wanting to let go with "life." It was fueled by the regrets of the characters; the things they never experienced in their life (such as Hurley finding a true love in Libby). Somehow, some one gave these lost souls the opportunity to live a second life on the island in order to experience those past events and maybe soothe their regrets.
If that is the case, then Jacob would be more like Clarence from It's a Wonderful Life than the Devil. He brought the people to the island. And the island gave them a second chance to find trust, love, friendship and a sense of purpose. It gave those lost souls a second chance before final judgment.