What is the main theme of the novel The Pearl, especially in chapter 1?

An overriding theme for John Steinbeck's parable of The Pearl is that of Good vs. Evil. This theme is connected to the theme of Social Class that begins at the end of Chapter I and develops further in the narrative.
Because Kino's people were once creators of songs, his culture produced many songs. And as a result, events and thoughts began to be frequently interpreted as various songs until these songs became part of the people's tradition. Kino, the main character, hears these traditional songs in his head. As he awakens in the near dawn, Kino glances at his baby and wife. When he hears the splash of the waves on the beach, he closes his eyes again so that he can listen to the songs of his people. The Song of the Family comes to his mind, and to Kino, the rhythm of the family song is the grinding stone that Juana uses. As she works, Juana sings an ancient song softly.
After Kino rises and the streaks of sunlight enter the brush house, Kino and Juana freeze in fear as they see a scorpion moving down the rope that holds their baby's box. In his mind now Kino hears the Song of Evil, the music of any foe of the family. Beneath this song, the Song of the Family "cried plaintively." As they watch the scorpion in fear, Kino can hear "the evil music of the enemy." When the scorpion strikes the baby, Kino beats and smashes this venomous enemy with the Song of the Enemy "roaring in his ears."
Kino starts for a doctor, but those outside tell him that the doctor will not come. Then Kino sees his wife's determined look and hears the music of the family in his head "with a steely tone." After he tells his wife what those outside have said, Juana insists, "Then we will go to him." They set out and pass the area where the peasants live and the city "of stone and plaster" begins as a procession of peasants follow them. They pass four beggars who sit at the front of the church and know everything that transpires in the town. They also know the doctor who is of the ruling class and is from France. When Kino tells the servant, who is also a peasant, why he needs a doctor, the servant instructs him to wait. After this servant informs the doctor that an Indian's baby has been stung by a scorpion, the doctor becomes angry, expressing his disdain for the Indian: "I am not a veterinarian." Then he instructs his servant to find out if the man has any money. When the servant returns with "eight misshapen seed pearls," the gatekeeper is instructed to tell Kino that the doctor has departed. He closes the gate quickly in shame for his falsehood, and Kino, too, feels shamed. Out of courtesy to Kino, the neighbors leave, as well.
This class distinction is something that sows the seed of the Song of Evil that prevails throughout the narrative. Unfortunately, Kino does not hear this song when he is sent away by the doctor's servant, nor does he recognize the potential for evil involved with his discovery of the huge pearl as does Juana.