A person is born at the lowest level of entirely egoistic desire, called “this world”. However, a person’s goal is – while still in his physical body – to pass the levels of all worlds and unite by his qualities with the Creator, with the highest level. To become like the Creator is the goal of the Creation.
A person can move through his desires/qualities inside these worlds/levels depending on the changes in his desires. As soon as the desires of a person become similar to desires of a certain level, the person immediately combines with it through his internal perception. This is because he coincides with its qualities.
Courtesy of http://www.youtube.com/watch?v=wMyslLCWhOE