Reincarnation

From spiritandsky.com:

There is a theory among those that believe in reincarnation that all life forms contain spirit. The spirit is born as a small entity, in the smallest of creatures. As lifetimes are lived, the spirit evolves, passing from one physical existence to the next, working its way up the spiritual ladder of evolution until ultimately re-joining itself to it's original creator. Then, possibly, the cycle starts over again.

The idea is not so much we are not worthy to go directly to heaven, but rather we are not ready... It is thought that lifetimes, in different forms, evolving upward, is the very reason for our existence in the first place. This theory makes all life connected to a common thread. It makes all life forms related, brothers and sisters if you will, on this seemingly endless spiritual journey we all must take. It is thought that the evilest of people evolve, or devolve, step back a peg or two in order to relieve, or learn spiritual lessons so they can resume forward growth. In this theory ALL are saved, and ALL no matter what, will one day rejoin the creator in the great cycle of life.

Reincarnation, if it's real, does not require your belief in it. It is thought to be as natural as a seed sprouting, growing, then dying. But is it real? That's up to you to figure out dear friend!