All of our souls have volunteered to come to earth to exist as humans, and God has put a price on this trip in the way of reincarnation for those that have not learned or that have not done good by God's word, so they will return again and again until they have done it all right.  Think of it as a video game that can never be saved, and will always be forgotten, so as you play, it must be done right the first time or else you are coming back again.  This also explains Karma, as unfinished business in previous lives will have to be answered for in this life.

People wonder why horrific things happen to good people, those people are paying for transgressions of previous lives.  There are checks and balances to be maintained in the universe.  It seems the only offset that does not have to be maintained is love.  Evil and death is answered with evil and death.  (an eye for an eye).  Revenge is evil, and is answered by evil, so "vengeance is mine sayeth the lord" is God exacting Karma on an entity, possibly not in this lifetime but later.  A balance must always ultimately be maintained.  Some good books to read on reincarnation is one by Edgar Cayce and a book called a dweller on two planets written by Frederick S. Oliver, who describes his reincarnated lives on earth and Venus.  How could someone live on Venus you ask?

An immortal entity does not necessarily need to exist in a 3 dimensional environment, there are many planets that have an existence in 5th and 6th dimensions, which are much friendlier environments compared to ours.  Actually, earth is an anomaly that is brutal and would be considered a real challenge to exist on.  To truly embrace Spiritual Enlightenment, past lives should be investigated.  It may not be possible for you to realize your own past lives, but it is easy to read about others.  More than likely, if you have problems with certain people or situations, those will be what you will need to focus on, to resolve any differences or feelings of ill will or animosity towards others or situations.  This will repair or equalize your karma, to allow

you to proceed to the next level.