I just started reading this book. And I was asked that question so the answer would have to come from the beginning of the book.
Kino has a close connection with Juana. It is very elemental in that it is closely related to nature, family and universal bond,
"Kino could never remember seeing them closed when he awakened. Her dark eyes
made little reflected stars. She was looking at him as she was always
looking at him when he awakened... In Kino's head there was a song
now, clear and soft, and if he had been able to speak of it, he would
have called it the Song of the Family."
Juana is Kino's conscience and guide. The pearl of course disturbs this balance.
