The soul is an immaterial substance - the supernatural, unexplainable. It is, by its very nature, am unknowable question. How can that be an answer by any reasonable definition?
If what we known to exist and understand can't explain all observed data (our thoughts and inner experiences) than we are forced to infer the existence of something outside our understanding.
Yes, but there is a difference between "outside our understanding" and "impossible to understand". There is simply no good reason to believe that consciousness is impossible to understand.