When a person dies, his or her soul loses its physical body, but dons a new spiritual body which is a sort of psychological duplicate of the one it left behind. Once the soul makes the transition into the mainstream spiritual world, it then gravitates to a position that is appropriate to its own level of spiritual purity. Any given spirit can, over time and by virtue of its own free will, rise to higher levels or fall to lower ones within the mainstream spiritual structure. In other words, their status within the spiritual universe is not static. Each soul acquires its spiritual buoyancy naturally. Saint Peter does NOT stand at the gate condemning some souls to Hell while others are admitted to heaven. Where you first land in the spiritual firmament after the death of your body and your decision to cross over into the mainstream sequence is a matter of spiritual physics!
The earth is not the only place where spiritual evolution can take place. Spirits evolve within the spiritual realm itself, and once a spirit has “crossed over” from the transitional plane into the mainstream of the spiritual realm, the planes of illusion are where most of them start. Once they have crossed over, positively developed spirits generally ascend to ever higher levels, and negatively developed spirits can go either way, up or down depending upon their own inclinations and the decisions they make using their own free will. The planes of illusion are like a spiritual high school in which spirits can advance to the next grade or be demoted to a lesser grade. The whole point, just like any school, is that everyone should learn their lessons and graduate. Whether they do or not depends on each student’s own free will.