what is the purpose of the epilogue at the begining of the novel?

The epilogue in the Pearl is more a parable than anything else. KIno and his wife return with their dead child, " There was no Song of the Family in that little brush house, just the Song of Evil, pounding incessantly against their ears as it had been for the past year." Steinbeck hammers home the themes, whatever the reader thinks they are, through a cautionary tale. Kino throws the Pearl back into the ocean and the story ends.