What is interesting about the character of Kino is the way that music is linked to any powerful instinct that he has during the course of the book. For example, when we are introduced to him in the first chapter, when he is happy and content with his life, he hears the Song of the Family. He hears the Song of Evil when he is able to detect hatred and deceit. The importance of music to his character perhaps reflects the oral nature of Kino's culture and how music and stories would have been handed down through the generations. Music is therefore key to how Kino voices his thoughts and emotions and is a key sign of what is going on inside of him.
It is also interesting to remember that Steinbeck never wrote this originally to be a novel. He was rather planning to make this into a film. In this sense, we can see how the musical tunes could have formed key motifs that would have been played for the audience to hear during the action that would have greatly enhanced this element of Kino's character. Music therefore is a way in which Kino is able to express his internal emotions and feelings in this text.