Matilda challenges our understanding of family as something good, loving, and safe. For most of the book, the families that we hear about—Matilda's and Miss Honey's—are downright dreadful. Miss Honey's aunt physically abuses her, while Matilda's parents emotionally abuse and neglect her. Neither Matilda nor Miss Honey is praised by their family members for their intelligence, or encouraged to pursue their education. But by the end of the novel, they've managed to forge a new family, with each other, and we feel pretty confident that this new family will be anything but dreadful. We're sure Matilda and Miss Honey will respect and love each other as any good family members should.
If Matilda hadn't had such terrible parents, she wouldn't have been as motivated to educate herself on her own terms.
Matilda shows that the most important family isn't the one you're born into but the one you make.