Some people theorise Reincarnation rests on the belief that after the death of the physical body there is some element left of each person that then goes on to survive. They begin another journey if their existence and therefore the end is only the beginning.
In my opinion I think that once separated from the body the soul becomes all intelligence. In our lifetime it would be very difficult to function if past lives were constantly being remembered. So I believe this is why the soul which the mind cannot touch with thought retains the knowledge if the incarnations and not the spirit.
When we die the two reconnect until the next life begins. I think that we are here on this earth to learn from the raw materials of physical experience. But because we have free will we make some choices which are not always wise and do not nurture our spirit and soul.
Reincarnation has been called many things
The cycle of rebirth
Transmigration of the soul