That's not a very good response since it assumes that everyone believes in the soul and also might understand how fiction feeds it. A better response is that fiction allows you to pretend, and pretending is the way we predict where complex situations are likely to move next. When you read fiction, you practice moving from the suggestions provided by the author's words to a richly imagined experience that relies largely on the details you supply yourself. To read fiction is to collaborate in building an elaborate model of experience.
When you read a novel, you make sense of the patterns it holds by imagining the experience it describes as though it were unfolding in your own mind (which, of course, it is). This is the same thing you do when you imagine yourself in a meeting or making a decision or facing bad news. It's the same thing you do when you imagine what you will say to someone the next time or meet, or how you would like to change your hair or your body type. Imagining in detail is the foundation not only of fiction, but of nearly every important decision you make.
Reading novels feeds rich and meaningful patterns into your brain so that you can compare them to real-life strategies, personalities, and relationships. It engages many areas of your brain so that your brain forms new connections and becomes healthier. It interrupts the patterns of your daily life and makes room for new thoughts, attitudes and states. It reinforces the complicated, wonderful connection that you have with other human beings and helps you see that seemingly random events and emotions can generate satisfying meaning.
That's what I mean when I say that good fiction feeds my soul: it wakes up my brain and offers me meaningful patterns I use to enrich my lived experience.
What are you doing that produces more benefits than reading a good novel?