I think the last line essentially means that along with the pearl, all of the hatred and greed that had affected Kino and his family also disappeared. In the beginning, Kino and his family lived a normal life, and they were happy. When they found the pearl, they thought that it was just a stroke of great luck. The music of the pearl then was beautiful and optimistic because Kino and Juana saw so many opportunities that could come from it. Kino wanted to use it to send Coyotito to school; if he made it, then he could lead the way for others. The pearl was his hope for the future. It was his way out.
When people found out about it, they began to get greedy. That was when things took a turn for the worse. The music of pearl turned evil and it became a burden on Kino and his family. At the end, when they flung it back into the ocean, the burden was lifted, and they were free. The pearl itself is something that's supposed to be treasured, not sold. When people try to use it for their own selfish purposes, it turns evil. When it was returned back to the ocean, it became good and the music was beautiful again. Kino and Juana were lucky enough to be able to hear a little bit of it before it disappeared completely and died away.
When people found out about it, they began to get greedy. That was when things took a turn for the worse. The music of pearl turned evil and it became a burden on Kino and his family. At the end, when they flung it back into the ocean, the burden was lifted, and they were free. The pearl itself is something that's supposed to be treasured, not sold. When people try to use it for their own selfish purposes, it turns evil. When it was returned back to the ocean, it became good and the music was beautiful again. Kino and Juana were lucky enough to be able to hear a little bit of it before it disappeared completely and died away.