Q: Is the soul fixed in the body, or does it change?
A: Let me simplify the explanation by saying that the soul is fixed and never changes, because otherwise one cannot even begin to understand what happens with the soul and compare its varying situations.
There is another basic question that comes up: if the soul does change, that would imply that one soul works, while another is rewarded. It is very hard for beginners to accept that, because they think it is unjust. But generally speaking, souls do change all the time. Each moment there is a new soul.
A soul is something indefinable; it is the corrected desire that constantly changes and unites with other parts of itself, other parts of souls. In the end, after having been corrected, all the souls will unite and be filled with the Creator.
Therefore, the differences between souls exist only in the sensations of uncorrected souls, meaning only during the process of their correction and only when they sense, through their natural attributes, where there is a demand “for me,” and perform the calculation, “Who does the work and who receives the pay?”