In my view, reincarnation exists or it does not. Not much differenent than the sun rising each day. The sun shines on all regardless of their moral character; it does not differentiate. Now the intellect might ask - What is the justice of this? The answer is that it just is.
If you assume nothing is static then each person can go up or down or a mixture of both in any one lifetime.
The issue of not remembering is profound. Suppose you could remember. Now overlay that on all of the issues within the physical, emotional and mental aspects from the acculturation of this lifetime. It is a blessing that most people cannot recall. Most people are challenged just dealing with the good, bad and indifferent of this lifetime. Only the more purified with good phsical constitutions are really suited to handle multilpe lives superimposing in this lifetime.
Couple these problems with the fact we life in H2O based living tissue bodies. A good analogy is someone going underwater and trying to discern what someone out of the water is saying. In other words, the messages are blocked or garbled or on the other side, the perception looking up is blocked by the cloud (moisture) cover that hides the Sun/Son.
One answer to the question of why people are not more evolved if they have lived multiple times in the physical is that it is easy to get dazed and confused existing consciously and usually less than consciously where the flux of duality obscures the inner reality. Plato's analogy of the cave sums this up pretty well.
As was said in Egypt (paraphrased): I am Isis, no mortal man has ever seen me unveiled. To get to the evolutionary state you postulate, one has to transcend their mortal nature while maintaining a physical body.
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