Previous parts in Theme-Worldbuilding are indexed here:
All readers, of fiction or non-fiction, are detectives working a mystery case.
First they want to know what this book is about, and why should I waste my time reading it. A closed book is a mystery.
Once hooked by your first line, your reader becomes YOUR READER. They have "entered" your world, they have invested themselves in opening the book.
At that point, the mystery becomes, "what are the rules of this "world" and how do those rules differ from the rules by which I live my everyday life."
A story becomes interesting by posing a question, and part of the intriguing nature of a question is the unconscious assumptions behind the frame of the question. Those unconscious assumptions behind your crafting of a first line are in fact the elements that frame your theme.
The theme of a work of fiction must be stated, baldly, in "on the nose" vocabulary once in a work of fiction, first at the end of the opening scene -- about 5% of the total wordage of the work -- and then near the end, right after the climax.
The theme is what the story is about, but whether the thematic statement is true for your reader has to be argued in the Worldbuilding part of your story, not in plot, story, character, action -- all of the other components of a work of fiction illustrate the theme, and the theme is the statement of the essence of the World your Characters must cope with.
The mystery the reader is working through is, "How does this fictional world differ from my everyday world?" And beyond that, whether the fictional world is an improvement on the everyday world -- or perhaps if the thematic thesis somehow illuminates or explains the everyday world.
The overall, core, theme of Romance is Love Conquers All, and beyond that, once "conquered" then All will deliver the Happily Ever After smooth glide through life.
In everyday reality, it's hard to see that happening to anyone, least of all yourself -- and very probably yourself while you are in love.
People who "fall in love" are usually astonished, bewildered, and experience the state of mind and heart as a "game changer."
Today, there is a lot of research going on focused on the brain, while even more money is being poured into research on the mind. Scientists are trying to prove that the mind is a product of the brain.
If they can establish this beyond doubt, then they will have proven that the hypothesis of the existence of a Soul is an unnecessary complication, and all human behavior can be explained simply as a function of the brain. Occam's Razor logic says go for the simplest explanation that works, so that will be the thematic basis of the science of the future.
To write SCIENCE FICTION -- and therefore to write SCIENCE FICTION ROMANCE -- the writer takes an idea that is currently unquestioned by science, something assumed, an axiom, or so well proven it may as well be an axiom. Then the writer builds a world around the premise that this axiom of science just is not true.
The mystery the reader is solving is, "How would the world be different if this axiom of science is not true?"
No single novel, or single author, can compile all the possible differences a shift in axioms might bring, so we have to select one possible consequence and build the entire fictional world around that.
The THEME is composed of A) the axiom that's wrong, B) the corrected axiom, C) the consequence of the new axiom.
Suppose science concludes there is no Soul, but in fact there are Souls, therefore the meaning of life has nothing to do with the appearance, or fate, of the body.
THEME: LIFE IS ABOUT THE LEARNING EXPERIENCES OF THE SOUL.
THEME: LIFE IS ABOUT THE LEARNING EXPERIENCES OF THE BRAIN.
THEME: LOVE IS AN ATTRIBUTE OF THE SOUL
THEME: LOVE IS AN ATTRIBUTE OF THE BRAIN
Whether Love can Conquer All might depend on whether it is an attribute of the brain, the mind, or the soul -- and that writer's decision is called world building.
Here is an article (which may not be true, but makes good fiction fodder) posted in Elite Daily:
If we really want to get technical, functional magnetic resonance imaging (fMRI) scans *actually* measure oxygen levels in the tiny veins in our brain, not just "the brain." For those of us who aren't literal brain scientists (hi), the take away here is that there's a lot to be learned from observing brain scans, especially when it comes to love. Finding "The One" has been linked to increased activity in the areas of the brain associated with sex, reward, and memory. And what's better? Being in love is also connected to decreased activity in brain sections linked to fear and dislike. So basically, being in love means more stuff is happening in the good places of your brain, and less stuff is happening in the bad.
And that is science completely about the brain. Is that all we are? Cells, and nerves, electrical signals? Or is there a Soul that science can't detect?
You might want to reread the 6 or more parts of SOULMATES AND THE HEA series:
If your thematic thesis is that there does exist a Soul, then your story, or your novel, would be about a particular Soul ripped, torn, mashed, stretched, and flung through a learning experience.
As you specify what Soul, starting where, going where, doing what, with which consequences, and what obstacles to conquer, your story emerges complete with plot, characters, situation, setting, etc.
Two good examples to contrast and compare are these novels:
Tanya Huff's Peacekeeper Series is one to watch -- #3 in the series, THE PRIVILEGE OF PEACE is about a second encounter with the defeated obstacle of previous episodes, Big Yellow, an alien spaceship which seems to mean humanity no good. It's a takeover attempt, invading the body-brain of humans, and doing more than just spying.
Now contrast/compare THE PRIVILEGE OF PEACE with C. J. Cherryh's 1997 entry in her MERCHANTER series, part of the ALLIANCE-UNION saga she is still expanding for us with the 2019 entry, ALLIANCE RISING (#1 in the HINDER STARS series). (note this was from Warner Books, not DAW, so it's hard to get since she went back to DAW as her main publisher).
"Finity's End" is the name of a starship.
I enjoyed re-reading FINITY'S END after that ship turned up, brand-spanking-new in ALLIANCE RISING.
So I puzzled over why I enjoyed this old story so much -- and concluded it was the meticulous world building that generated the vivid, deep, torn and tormented Characters, shattered by war and loss of those close to them, but now healing, re-connecting, creating a new vision of a better future.
Tanya Huff deals directly with a sexual love bond, while Cherryh explores the strife/strength axis of family bonds -- great-grandmother, cousins, aunts, etc. extended over (rejuvenated) lifetimes complicated by the time-dilation of FTL travel.
But they both write in universes where the Soul is a real component of the world building, while the Characters (just like us) have no clue about that and don't want to know.
This world building technique (what the Characters don't know about their world and aren't curious about) lets the reader either see it's there or firmly believe that it is not there.
Ambiguity is one of the most difficult aspects of Art to master, and both these writers have achieved that.
But in both these novels, you see that ambiguity used in broad strokes to great effect.
Why does love matter? Because, whether there is a Soul or not, Love reconfigures the brain and that changes what you do, when you do it, why you do it, and even whether you'll do it or not.
Love configures behavior by reconfiguring the brain.
Since the brain is so plastic, so impressionable, it is entirely possible that love could be reconfigured out of the circuits. And therein lie a lot of novels. The question could become, "Can love conquer the obstacle of its own lack of existence?"