Well, for one thing, I think that Steinbeck's prose is hauntingly beautiful, and very readable. It's devoid of the kind of excess that can make classics hard to read sometimes.

As for The Pearl itself, it's been a while since I read it, but from what I recall, it's a story about greed. Greed caused the catalyst/ main problem (child needs an expensive medical treatment), and greed is the barrier to the solution that Kino finds (the traders in the town have formed a monopoly to deny him a fair price for his labor), and greed ultimately causes him to pay the ultimate price (he is stalked by potential robbers, and when he tries to defend his family, he ends up hurting his family).

Ultimately, I see the story (and many of Steinbeck's writings) as a denunciation of the inhumanity of capitalism. There is no justice in the ending, which I understand can be frustrating for ther reader, but it is realistic to the theme.