Why does the book open with a firefly in Chapter 1?

The book opens with a charming image of our heroine Melody in her wheelchair enjoying the visual delight of fireflies, One lands on her hand and seems to look right at her. She asks what he is thinking and on cue, the lightning bug fires up its glow as if sending her a signal. She asserts that Mr. Firefly was answering her because, after all, she knows all about communicating with speaking. The firefly is a complex symbolic incarnation of Melody herself.