Why is this gonna happen?

First and foremost we still do not know if anything at all will happen on December 21 2012, or at any time in 2012, or indeed at all. We will examine that more closely in just a moment.
But quite simply, if, and only if the prophesies are true, then one of three fundamental situations will likely result immediately before, during and after the 2012 event based upon what we know to date:
1. Human beings will undergo a massive Spiritual evolutionary transition whereby true, Divine, Spiritual reality will be realised and experienced. Focus and abilities will no longer be materially based, but rather Spiritually based.
If this comes to pass, humans will still inhabit a physical body, but the body will assume its true identity as a vehicle of learning. Material things will be seen for the illusion they truly are, and the emphasis will be on "service to others before service to self", and the building of the biblical "kingdom of heaven on Earth", a paradise where selfishness, war and disharmony will be a thing of the past.
2. The Planet Earth, a great, living planetary Spirit, will evolve or "graduate" to the 4th density, the next evolutionary level on His/Her own path of return to The Prime Creator. In this case all organic life on Earth will cease to exist, and will also transition to the 4th or 5th density, the Astral or Spiritual worlds, where life will continue as ever in the Astral or Spiritual body, depending on Spiritual progress.
3. Earth will experience some massive cataclysmic physical trauma which will destroy most if not everything on the planet. If this happens the result will be the same as in possibility 2. above but will happen in a different way. It is likely that all life will transition to the 4th or 5th densities, again depending on Spiritual evolution, before this cataclysm strikes, so there will be no suffering.
We are not intended by the Universe to suffer; all suffering is a direct result of the actions and thoughts of humans.
The most important potential outcome is the evolution of present day human beings; Homo Sapiens, to the next level: "Homo Spiritus".
So the big question is; will 2012 actually happen? Do we really only have just over 6 years left on this planet? If so, what do we need to do in those 6 years?