Each of us is a soul. We have been told that we "have" a soul, but that's not the same thing. To have a soul would indicate that we are primarily an ego or a personality that in some way "possesses" a soul. Our essence IS the soul and all aspects of ego and personality flow from that essence. At its core the soul is pure, but habits, tendencies, and imbalances often obscure some of that inner light. Our spiritual work is to correct whatever shortcomings may be preventing the light of our sould from shining through.
The dark night of the soul refers to an extended period of acute purification that a spiritual practitioner undergoes immediately before making the final transition to deep spiritual awakening. It emphasizes purification and the act of letting go of what no longer serves after many lesser trials have been navigated.