Take care of the sense, and the sounds will take care of themselves.
Here the Duchess actually lands on good advice. Juxtaposition contrasts sense with sound—meaning before music. The confidence fits a maxim delivered like a kitchen rule. Thematically, it counters Wonderland’s style-first culture. Alice is learning to anchor herself in sense, even while enjoying play. The line resonates anywhere words risk becoming decoration. Keep the truth; polish can follow.