The Pearl is quite different from most of Steinbeck's other works. While he is a master of creating interesting stories and complex characters, he was very disillusioned after World War II and became more concerned with a more philosophical approach to figuring out the meaning of life. So, in this novella, you will find a parable, similar to Hemingway's The Old Man and the Sea. In spite of his non-Christian world view, there are a lot of Biblical images in this story. It is about a man who is destroyed by greed. He finds "the pearl of great price" but the love of the pearl makes him forget the important things in life, like love, his family, etc. No earthly treasure is worth the price that must be paid for keeping the pearl, in this story.
In this story, the pearl diver, Kino, has made the pearl his idol and it becomes more important to him than the original purpose of why he wanted it, which was to pay for his son's medical care.
Read about it here on eNotes.