Throughout the years of Lost, it was thought that the polarities of the show were good v.s. evil. And this may still be true. The beauty of it is that Lost has always been wonderful at skewing the lines, and always finding the gray area. This is the meaning I found behind the show and though I think some will disagree, I'm certain that there is something to this.
Lost was about meaning and not objectivity. Christian Shepherd told Jack that everything that ever happened to him was real(and this is in a way a metaphor for the entire show). We can't really find absolutes in life, and meaning is what is most important. The two core polarities of the show were symbolized by Jacob and MIB(the man without a name). People throughout the weeks were very angry that MIB was never given a name; but there is definitely a reason he wasn't given a name. Jacob represented existentialism. He believed in choices and meaning. He lived an extremely long period of time, and he saw the subtle connections between things and how everything influenced everything. This was sort of symbolized by his "touch". MIB on the other hand never had a name; and this was a very important symbolic gesture by the writing team. MIB symbolized nihilism and meaninglessness. If he were to escape the island everything would "seize to be".
The island itself was sort of like a dream world(though as mentioned earlier, the lines between dream and reality are skewed in Lost, which mentioned earlier is the entire point of the show.... "What Happened ,Happened". Realism and objectivity are meant to be left at the door when analyzing the true meaning of Lost, as it's more of a subjective experience. The island is sort of a place in the realm of possibilities that people's concepts and subconscious conflicts are played out on the grand stage(think dream interpretation where subjective concepts have a certain correlation with the objective objects within the dream world).
Reincarnation plays a big part in the show. The alt realities symbolize reincarnation. And this is where concept of the "Constant" becomes so important to understanding the dynamics of Lost. The "Constant" represents a consistency in each possible reality that never changes. It is depicts the true self, what has to be identified to achieve self actualization. It is the love or the true identity that everyone is searching for every time they are born onto the earth. Some of the survivors constant was their "soul mate". This didn't really cut it for Jack though, because Jack didn't really have a true soul mate that was perfectly matched for him. Jack was looking more for a home, a place where people would believe in him. In a way, everyone was his soul mate. This is why he flashed when he placed his hand on the casket. What he was looking for in his father, he found in the rest of the survivors; people to believe in him. The whispers on the island were souls that were still searching for absolution from their conflicts.
To understand what the island meant on the most basic level, one must understand what the numbers were. 4,8,15,16,23,42.... which add together to equal 108(the divine number, which is supposed to symbolize self actualization). Since the numbers symbolized the castaways, the numbers showed the perfect formula through which the castaways would reach absolution.... together. One could possibly deduce that the island was made by them, a world that the souls created together to find each other; this is one of the wonderful things about the line of objectivity v.s. subjectivity that Lost skews(which in life theres always debate, and there's always a skewed line between what is real and isn't real......a sort of relativity dependent on the observer).
Throughout the show there were little clues of how everything fit together. The hatch computer being one. The castaways had to put in the code to reset the number every 108 minutes(the divine number). 108 in this situation represented divine potential of the castaways together, and each time the number was reset it represented reincarnation. The hatch computer was a representation of life and how you start out with a chance of finding yourself, but as time dwindles away. Each time the castaways had to put the solution in to start over the sequence; not realizing that there was a divinity between the numbers(which represented them not realizing the divinity between themselves and how all the pieces of everything interconnected). John Locke refusing to push the button depicted the nihilism setting in.
The others(which were named the others for a reason) were supposed to symbolize foreign influence; which is sometimes needed to realize someones purpose and destiny. At times they almost came to the point where they appeared tribal. At the source of everything though, they were just like the survivors(searching for answers); which is why they had homes and air condition just like what the typical person has in civilized society(and the writers made sure to emphasize this).
The Dharma Initiative symbolized exactly what they were on the show. Scientists, searchers of the unknown; looking for clues..the whys and hows. Dharma in eastern philosophy means the path that one most follow to achieve liberation. Which is what the Dharma Initiative was trying to do, find answers; and for some especially Sawyer and Juliet was the path. The civilized path, the one where they settled down and lived the 9-5 together.
The light at the center of the island symbolized exactly what the character "Mother" said it did; existence. "There is a little bit of the light in everything" and if it went out there would be nothing. Those that said "Across the Sea" disappointed, did not understand the full context, and many still don't. The island was the internal conflict and redemption of the castaways played out symbolically under the spotlight. It is about meaning and finding answers. "You needed them, and they needed you." "To remember and let go".