You might be the writer who doesn't need summaries. You're probably not, since you're not the Almighty. Only the Great Maker could skip the step of telling people what the creation was promising. The stories that started the world were formed when there was nothing else to watch or read or hear. You and I do not have that deal. We need to sum up what's in our books, whether they're finished or just begun.
It isn't an easy task to sum up. I learned it at the copy desk of The Daily Texan. I wrote headlines for things I'd just read on the wire service. Headlines are like titles, delivering a lot in a tight space. Give us the essence of what happens. I like using titles for my chapters, whether in a nonfiction book or a novel.
Summaries serve your writing before it's finished. They can help you finish, because the summary will be shorter than the book it describes. A summary tells the readers three things
The needs of the characters
The actions the characters take
The intentions of all in the story
Immigrant housekeeper Anna serves two Catholic priests at their rectory. One of the priests is a new addition to the parish, so Anna believes she must impress him with her skills to retain her position.
That's about her intention and need. Then we move on to what's taking place.
She hovers in line at the butcher, angling for the best cut of meat to serve for the new priest’s first Sabbath supper. The butcher sizes her up as always, treating her like something from his case. She rebuffs his leering and comes away with two fine roasting hens. The butcher's line reminds her of the worst parts of desire.
Those are things happening in the first chapter of my current novel. The actions lead me toward the scenes that reveal the events.
You also need sweep, to cover the entire story for summary.
It's 1901, a time when the Rust Belt sparkles. When rectory housekeeper Anna falls in love with Father Joe, the priest fathers their baby. She wants to turn their sin to joy to match the gladness in her heart. They will be a new family. He leaves the priesthood to make a life with her. But poverty and illness drive them apart, so she must start anew, battling a bishop to protect her son and pursue women’s liberty.
This is revision, over and over, winnowing the writing to show readers the essence of something very large in a much shorter space. Nobody wants to write outlines, but nearly all of us need to. The outline can be as simple as one crucial action per line.
K.M. Weiland says in her 176-page guide Outlining Your Novel to stay loose while you create a summary and outline. Use a pen and paper to remind yourself this is as playful as writing a scene on the keyboard. Learning to summarize your work is crucial to your getting help with it from editors or beta readers. Practicing summary is also the heart of a good query letter, and the soul of a good book description.