Answer: One soul refers to the fact that we are all parts of one desire, which according to its volume and its power resembles the Creator. Initially we are in an egoistic state, which means that we want everything only for ourselves.
We all have to correct ourselves so that we will want everything with the intention of in order to bestow. To whom? If the desire is one and we are all part of one desire, we have to bestow unto the Creator.
When we give and bestow unto the Creator, the Creator gives and bestows unto us, and we become partners and connect in mutual bestowal to each other which is called Dvekut (adhesion).
This is actually the state that we have to attain. This is the reason that all of mankind, being parts of one soul, need to help each other to reveal it, attain it, and reach the state of eternity, wholeness, and infinity, just like our Creator.
From KabTV’s “A Talk About Soul” 3/30/17