I’ll use one of my favorite novels, The Flowers in the Attic, by V.C. Andrews as a basis for the answer.
What is the Plot: Four children are abandoned in an attic awaiting the death of their grandfather.
What is the Theme: Family relationships (mother and child relationship/abandonment), struggle against societal pressure (the mother’s place in society was far more important than her children), man’s struggle against nature (greed, sexual desire, inner demons)
Theme is not preachy and in your face. Even Christian authors can write great fiction without preaching to their audience, think Dekker, Peretti (see below). All fiction should have a theme but that message should never be shoved down the reader’s throat. It should be intricately weaved into the plot of the story. The reader should read the entire story then realize, “Oh, what she/he was saying was …”
My examples of great themed books:
House by Ted Dekker and Frank Peretti (Christian supernatural) – Man’s struggle with divinity, family relationships (Jack and Stephanie are going to counseling and considering divorce), Death (Jack and Stephanie’s daughter died and they are struggle to understand), man’s struggle with nature (they must kill one of the people in the house or the crazy serial killer, Barsidious White, will kill them all and they struggle with the decision)
Twilight by Stephanie Meyers (YA paranormal) – never judge someone based off stereotypes (all vampires are bad- per Werewolves; all werewolves are bad – per Vampires – until they have to work together), love can come in many forms be willing to accept it (Edward’s struggle against the love he felt for Bella), man’s struggle with divinity (Edward’s refusal to believe he has a soul).
Common Literary themes:
Love; unrequited love, forbidden love, love conquers all…
Family relationships; mother and daughter bonds, abandonment by family, failed marriage …
Man’s struggle against nature; the struggle to remain youthful, sexual struggle, inner demons, death…
Struggle against societal pressure; peer pressure, unfulfilled dreams, the American dream…
Yin and Yang; something good happens then something bad happens to balance it all out
Can you think of more themes? What is the theme of your story? If you don’t know how to answer that, you’d better make some changes to your MS. Every story needs a theme.
Have a great day. Read a book and laugh.