Strong characters and strong stories often have subtext*–the story underneath that tells us more about our humanity, in some instances, than the main story. I think this is especially true in horror stories. At the front we have something sinister, horrific, terrifying, but the subtext may explore human psychology: how loneliness drives one mad; our common, shared fears; spousal abuse; sexual abuse; any number of other themes.
When I was very young, maybe 11, I was reading a horror novel that my older sister had read. It was about a fragile woman who married the seemingly perfect man who was a (literal) monster. I remember my sister asked my about the moral subtext–which I had never understood. She explained to me that it was about abuse and mistreatment of women. I have loved reading for subtext ever since.
Subtext is sometimes joked about with horror, slashers especially. Have sex or smoke pot and the (masked) killer must impel you with a machete. The subtext is you must be chaste and pure to survive; bad people deserve to be punished.
I tend to often ask myself, “What is the subtext?” of my writing, as I also think of this in simple terms as the “moral of the story,” though it is implicit. Sometimes when I sit back and look at my writing from this angle, I say, “Oh, my, I certainly don’t want to say that.”
In the end, I think it is important to sit back and take a hard look at what might be brilliant prose, snappy dialogue, suspenseful scenes, and developed characters, and try to read the hidden message–and ask is this a moral I want to express, is it how I feel, believe.
*Subtext can refer to underlying themes or intentions, including in dialogue. I am using a narrowed definition to address underlying overall moral themes in fiction, and not character subtext, dialogue subtext, or scene subtext.