If we pare away the clutter of the various island mysteries, what were the key elements of the Island?
1. "Unique electromagnetic properties." This was stated numerous times by various people, including Dr. Chang and Faraday. We have seen the electromagnetic properties in action when the Hatch became supermagnetic when the lockdown began; in the light cave; and when Flight 815 was ripped in two at high altitude. There is also a question whether the smoke monster is a manifestation of the electromagnetic energy "polluted" by the dead soul of Jacob's brother.
2. "Time travel." We saw that the island and/or certain people on the island "flash" to various time periods. These flashes happened at different locations: in the FDW, the Hatch, in the jungle, on the Ajira flight, and at the Jughead cliffhanger. What was inconsistent was who would time skip. The Others, including Alpert, did not time skip when Locke and the Other 815ers did after Ben turned the FDW. Only a few passengers in Ajira plane time skipped, leaving another O6 member, Sun, from reaching 1977. Then we had the concept of mental "time skips" with Desmond's premonitions, which one major one (Claire leaving the island with Aaron by helicopter) turned out to be false.
3. "Being cloaked." We were told on numerous occasions that the island is difficult to find. Eloise set up a complex pendulum machine in the church basement in order to find it for the O6's return. Widmore had been looking for the island for years after his banishment. It would seem that the island's time shifting properties also includes spacial aspects of dimensional travel.
So we have a concise formula:
Island = EM + time + space
Let us re-work the formula to try to find some answers.
EM = time + space/Island
Time = Island/EM + space
Space = Island/EM + time
Further, take out the variable of the island itself.
EM = time + space/EM + time + space or EM x (EM + T + S) = (T + S)
Time = EM + time + space/EM + space or T x (EM + S) = EM + T + S
Space = EM + time + space/EM + time or S x (EM + T) = EM + T + S
Rewording the substance of the calculations:
Time multiplied by the energy and space equals the Island.
Space multiplied by the energy and time equals the Island.
Energy multiplied by the Island equals time and space.
The island and its power source (EM) create time and space. The Island is like the TARDIS in Doctor Who, an intelligent machine that can travel in time and space, manipulate and generate matter, shield and cloak itself, and defy the laws of nature and physics.
This would explain many aspects of the Island. It would explain why the Island was hard to find, because it did not want to be found. It can shift the space dimensions around it to become invisible. This would explain why when the Island "disappeared" after the freighter explosion it only caused a ripple on the ocean's surface and not a huge air pocket and massive displacement of water because it is not an island but a machine.
If the island is a space and time machine, it would need a pilot in order to serve its purpose. That may be why the Island needs a human "Guardian." It would also explain the mystery in time why Jacob was immortal. And what would be its purpose? We were told that the world would end if MIB escaped the Island. If MIB is at its core the energy needed to maintain the Island's functions, then the warning would be true. So the Island, as a machine, is critically important in maintaining the Earth's balance within the universe.
In order for humanity to survive on Earth, the planet's position to the sun, its rotation and electromagnetic polarity must be maintained otherwise the atmosphere would escape the gravitational pull and the sun's radiation would bake the planet to dust like Mars.
We can speculate that the Island is a regulator to keep Earth in the proper balance and alignment in our solar system. The masters of the universe created a machine to keep the cycle of life on planet Earth going forward in order to save the human species much like one puts an air pump and filter in a fish tank to support the aquarium's life.