I happen to enjoy a cappella music. Something about humans producing all the sounds of music, including the ones made by instruments marvels me. One of the interesting things about it, though, is how much of it is often overlooked.
When you listen to a cappella music, you gravitate toward the lyrics, or at least to the voice that is singing words. We're used to doing that, so it is natural. Nobody listens to the guy who is just doing the bass lines, or the guy who is doing a plain beatboxing rhythm. However, if the lyrical singer was singing solo, he wouldn't sound nearly as good.
So much goes on simultaneously that makes a cappella music sound good. You as an audience member may not be aware of it, but if any of those parts is absent, you will definitely notice it, or at least notice that something is off.
Writing functions similarly. People tend to notice the words in a story, but they often overlook what those words are doing. They create a mood and paint the emotions of your scenes. They do it by the synonyms you choose for any given concept (upset vs. frustrated vs. angry vs. mad), the length of your sentences and your paragraphs; they do it with your choice of smooth words which flow off the tongue or short staccato words that halt readers.
As always, be aware of the nuances of every word in your lexicon. Know how they function by themselves and how they function in conjunction with other words. It's a tall order to fill, but you can do it, and you will be a better writer for it.