What is significant about the fact that the Song of the Family becomes "a battle cry" when Kino and Juana return with the pearl and the body of their son?

When Kino and Juana come back from the battle in which Coyotito is killed, there is no "Song of the Family" any longer. Kino is filled with sadness and a sudden realization that his Song of the Family has been perverted by all of the evil forces in the world, from the racist doctor and priest to the merchants who want to cheat him. He will now face the world as a man who has battles to fight and who will, in all likelihood, no longer live in peace with the world. He is now a warrior in the world of reality, a world with which he was unfamiliar until his discovery of the pearl.