The "not two" of nonduality poses that although manifested bodies appear separate, they are all One. Countless sages have proclaimed this the fundamental reality.
However, sages are not in agreement on the issue of souls, reincarnation and Karma. Why not? It appears that some have had direct experience of past lives, and some have not.
For those that have, Karma and reincarnation make sense. For those that have not had such an experience, Karma and reincarnation are irrelevant. They point to the actual nondual nature of reality. What more could you want? Why get into those details?
It is already a big step from duality into nonduality. This step requires that one knows that all bodies are one, despite the evidence of the senses. This knowing is huge. Is it any bigger a step to postulate that souls travel through various bodies over time? If many bodies are part of the One, souls also are part of the One. Both are equally outrageous to the five senses.
A human being learns only so much in a lifetime. The level of human consciousness has remained rather stagnant over millennia. It would stand to reason that it would take the average person many lifetimes to really change, grow, and learn the truth.
If we are here to learn, to grow, to rise above ourselves, certainly more than one lifetime would be required. Isn't it clear that certain individuals have risen far above the heap. How is this best explained?
Reincarnation is certainly the best explanation. A soul that has traveled through more lifetimes would certainly be more experienced, would have had more opportunities to learn, and would likely be at a higher level of consciousness. More experience, more lessons learned.
Haven't you known young people who seem to be wise souls? Aren't there many who seem wise beyond their years? Is it not the youth who often rise up and require change? Is it really far out to believe that they may have the advantage of having been here more times?
If there is a soul that travels though various bodies over time, then the concept of Karma comes in very well. Just as a person's current reputation precedes him, just so, a soul brings with it the weight of the good and bad from previous lives. This certainly explains why a particular life may seem lucky or tragic. The trajectory is in effect.
Karma helps relieve a lot of tension around the question, “Why me? That lives are the way they are may not be accidental, but the effect of previous lives. Just as the sins of the father are afflicted upon the son, just so, the sins of your past lives may be affecting you now.
I have tried to make three points.
One, that it is no bigger leap to believe that souls travel through various bodies over time than to believe that many bodies are actually appearances in the One.
Two, that souls are appearances in the One, just as bodies are appearances in the One. Non duality is actually a bigger leap than believing in reincarnation.
Three, Karma is the result of each soul's travel. The soul is the real traveler, changing bodies for a different view, and gathering good or bad energy along the way.
In the end, whether you are a soul or a body, you can be nothing other than the One. You are both.