Writer Anne Sexton advises other writers to put their ear close to the soul and listen carefully.
As an editor, I find there's a distinct difference between writing where the souls of characters are being examined and attended to by the author and writng where they aren't. I've edited some interesting manuscripts where there's good plot and suspense, good dialog and description, but the writing doesn't move me. It's interesting but it isn't profound, and I've realized it's because it doesn't go deep into the character's being but rather skates on the surface of actions and words.
A step up from this are stories in which the main character's soul is of interest to the author and he or she delves deeply there but all the rest of the characters remain superficial as if there isn't room in the story for their souls as well.
Then the most satisfying are those where we listen to the souls of most or all of the characters. We see their souls communicate with each other, we see the darkness in them and the light, we see the fears and joys.
Of course, some readers, perhaps even many, aren't interested in this depth of communion, hence the popularity of genres that remain on the surface of life. But I can tell you as a writer and editor that writers who can go there get my vote every time.