What does this quote from the book The Pearl by John Steinbeck mean?: "And, as with all retold tales that are in people’s hearts, there are only...

The key to this quote is that it applies to "retold tales in people's hearts." It does not say, simply, that there are only good things and bad things, good and evil, etc. It says that as it applies to retold tales, things are framed in terms of these dichotomies: good/bad, good/evil, black/white. This suggests that people tend to understand all things in terms of these binary oppositions. Something is good or it is not....

The key to this quote is that it applies to "retold tales in people's hearts." It does not say, simply, that there are only good things and bad things, good and evil, etc. It says that as it applies to retold tales, things are framed in terms of these dichotomies: good/bad, good/evil, black/white. This suggests that people tend to understand all things in terms of these binary oppositions. Something is good or it is not. A role is prescribed for a woman. If it is not, it must be prescribed for a man. This can be a useful way of understanding the world, but it is often oversimplified.

But this story is a parable. The narrator informs the reader that the everyone will take his/her own meaning from this story. Having already stated the tendency for people to frame things in terms of strict oppositions (good/evil), the reader prepares to read a story where the distinctions between good and evil should be clear.

So, Steinbeck warns the reader that this is a tale about the distinction between good and evil. But there is the possibility that he is also challenging the reader to see degrees of good and evil, or at least to look for instances where the distinction between good and evil is not so clear. The pearl itself initially represents hope and happiness, but it becomes a symbol of evil. So, the main object/symbol of the novel is somehow both sides of an opposition. It is good and evil. This contradicts the opening quote if that quote suggests that good and bad are always opposed.

In terms of characters, each person is capable of good and evil. Like the pearl, each person has the potential for one side of the opposition (or some degree in between). Kino understands the world via certain "songs" and he thinks of these in terms of good and evil. But he does not initially recognize that the pearl should essentially have a song of hope as well as a song of evil.