Symbolism, Imagery, Allegory
Let's talk about Sabriel's bells for a minute. Her set of necromantic bells, passed to her by her father, is the most important tool of her trade, in addition to being a dramatic fashion statement, worn on a leather bandolier:
Seven tubular leather pouches hung from it, starting with one the size of a small pill bottle; growing larger, till the seventh was almost the size of a jar. (1.62)
Each bell has a different function, and an associated sound. Ring one, and it puts everyone to sleep; ring another, and it banishes everyone who hears it deep into Death, including the ringer.
The tolling of Sabriel's bells can signify death, sleep, binding, enslaving, or casting someone free—but whatever the intended action, the noise of these bells is one of the most powerful magical forces we encounter in Sabriel's adventure. Because of this, each bell represents whatever power it particularly possesses, in addition to power in general.
We're reminded of John Donne's famous phrase, "for whom the bell tolls," also used as the title of a Hemingway novel, or the ringing of church bells—there's something final and inescapable about the clang of a bell. So bells don't just represent power in this book—they represent absolute power.