I think that the last sentence is saying that just as soon as the Pearl appears it is gone. It is back where it belongs in the sea. It has gone from being this big problem to being peaceful again back in the ocean.
The pearl itself represents hope. Kino first gets the pearl and there are a bunch of new opportunities for him. He could put Coyotito in school and get a rifle. I think that it is the people that make the pearl represent greed in evil. It is what they do that makes this happen. The actual pearl is peaceful and represents hope and new opportunities.
The music of the Pearl was evil because when the family had the Pearl bad things happened. The music of evil was a repeated motif in the story. Kino also heard it when the scorpion was in the house and Coyotito got stung. And now he is hearing it more and more with the pearl. It took Coyotito to be killed for Kino to understand that the pearl only brought evil.
I think that the pearl represents greed because Kino is a very nice, and calm man. Then the pearl comes into his life and it completely changes. He wants all of these new things that normally he could not afford. He will not give up his fortune even though bad things are happening. Kino changes and is no longer the man that he used to be.
Everyone was trying to get a part of the pearl. All of the villagers hoped that in some way Kino would think of them and share his fortune. They were also greedy because of the pearl. Some people were doing horrible things just to get it. They ruined Kino's property and they attacked him. All of this happens as news spreads about Kino finding the pearl and then he throws it back and the evil is gone. Kino is no longer linked to the pearl.
