Souls relate us to the cosmos and contain two major areas - the universal and the part that pertains to you individually, connected via a plethora of conduits. Why we need this/why it works that way is beyond comprehension. We can only speculate. These are just my beliefs, though, shared by a few, while others try to explain soul and meaning differently.

What's interesting is those who believe in past lives (that assumes continuity of souls). For them in their terms, they're lucky. New souls are created all the time. In 1950 the population of the world was 3 billion. Now it's almost 8 billion.
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