Words carry a great deal of power in The Wee Free Men, and not just because the Nac Mac Feegles are weirdly intimidated by them. The Nac Mac Feegles totally believe that words carry a certain kind of mystical power:
"They think written words are even more powerful," whispered the toad. "They think all writing is magic. Words worry them. See their swords? They glow blue in the presence of lawyers." (4.169)
But it's not all in their imagination—in Fairyland words have a lot of power. Tiffany can even summon up a sword with her words when she enters a drome's trap, and she sees that the Queen is able to use her words to construct the world around her.
Words also have a great deal of impact in the real world, though. When Tiffany thinks back to all the times that her grandma helped the people in the village, sometimes all she did was use words. She used words to tell the Baron that he should be kinder, or that there'd be a reckoning if he didn't watch out. And her words worked to create positive change, to make the world better.
It isn't just in Fairyland and the Chalk that words have the power to improve or destroy worlds. Nope—it's in books too. We can understand The Wee Free Men as a world in its own right, a place we step into one the first page and don't truly exit until we read the end. And what are the primary materials used to build and maintain this world? Words. So the power of words within the book can also be seen as a shout-out to the power of words more generally in our lives, which we think is pretty cool.