Your novel is ahead of its time. This means that no-one is equipped to understand it, because in order to understand it’d they’d have to have read it, and no-one has yet read it because – when they try – they find they’re not equipped.
A very vicious circle, this.
However, your work will be a sensation, eventually. Probably posthumously. During your lifetime, it won’t even be published. But you know you’re good, don’t you? More than good. Great. You sense it. That’s all you’ve got. Be satisfied with that, if you can be.
It’s Not Original Enough
Publishers are looking for the reasonably familiar that can be marketed as the unfamiliar because it’s just unfamiliar enough to pass. Until the genuinely original comes along and unexpectedly sells a vast amount, therefore creating a new reasonably familiar thing.
It’s Just Missed Its Moment
Your novel is perfectly good. Moving, well written, entertaining. It would have been published three years ago. Perhaps even two. This year, though, it just isn’t what publishers are looking for – because they’ve seen its like, and seen its like not do fantastically well. Perhaps you took the sensible approach, and wrote in a way that was similar to what you saw being published. Unless you’re very lucky, and things stay still for two or three years within your genre, this isn’t really a sensible approach. Writing a novel is not a sensible thing to do anyway. Genres don’t stay still.
It’s Missed Its Moment by a Few Decades
A lot of people, in starting to write, mistake being authoritative with poshing up their language. This makes their tone out of date, condescending, distant and is likely to put off publishers because they know it will put off readers. The voice of most novels now is not one that hovers, dissects, sneers. We tend to be down with the characters, in their bodies, in their dilemmas.
It’s Too Slow-Paced
I don’t mean it’s not a thriller. The best way to test your novel is to take down from your shelves five novels you think are similar in your genre (you should have at least five). Now, read the first five pages of each and see how many narrative possibilities have been set up. Does your novel have an equal number? Published writers are jugglers who generally keep five or six balls in the air; if you are only keeping two, you need to get better at juggling.
It’s Got a Point
An anger, yes. A sense of wrongness in the world, fine. Something the plot is constructed to demonstrate, no. This is off-putting to publishers, because they know readers will be ahead of it from the moment they start reading. If your accompanying email says that you’ve written a novel to counter global warming, you’re getting the formula rejection before tea time.
It’s Full of Bitterness
It is very very easy for your second and third novels, after the first has been rejected (if it has, as my first novel was, and my second, and my third, and my fourth, and my last but one), to become allegories of rejection. (This also happened to me.) These will feature a main character who is inevitably right surrounded by minor characters who are only there to be wrong in painful or amusing ways. Bitterness is corrosive. Within a novel, it eats through everything else, like the blood of the Alien, leaving what’s behind it softened, edgeless – it becomes its own motive. Novels are about understanding, not demonising. Novelists, unless they are satirists, are moral relativists – they can’t afford not to be. If the righteous are right, within a novel, then it’s a pointless exercise. (In contemporary Western novels, a character’s sense of righteousness is almost always a sign of their essential wrongness.) Certainty only exists within the compass of one point of view, and if you’re depicting a plural world then most of the people in it are partly right, partly wrong.
It’s Full of Love
This is similar to having a point. You loved your characters so much when you were writing them that you didn’t really want anything all that terrible to happen to them. So it didn’t. Not really. They pootled along for a while, they suffered a bit, they patched things up. But readers read novels because they want things to happen, including terrible things (perhaps especially terrible things).
It’s Just Not Finished
Experienced novelists often take years to write each book. There’s a reason for that. Sometimes a book needs to be left alone, then returned to months later – months during which the writer has written something else, so as to become a better writer.
It takes a long time to learn what a finished novel feels like. But if you go back to something you wrote that you thought was finished five years ago, you’ll probably see that it needed more work.
Of course the main reason your novel might not be published is that you gave up on it part way through. And that reason, at least, is something you can do something about.