What's the point if you don't remember what happened and what you learned in a past life?
I never understood why anyone would believe that one.
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The whole point is that you don't usually remember past lives because your memories in this body are only from birth, or early childhood. If you could remember all you have done in past lives it might drive you to distraction.
Mercifully we are protected from the actions of lives we cannot remember when we were less spiritually evolved.
We might have been barbaric in past ages and now some of us are more spiritually developed. We still have to account for all past actions but the details are dealt with by the angels of karma who select the experiences of our current incarnation to settle karmic debts we may owe. The angels of karma are a separate species that never incarnate, and whose job it is to guide the collective souls of mankind to evolve.