What morals or lessons can we draw from the strange case of Dr. Jekyll and Mr. Hyde?

I think the story speaks to the duality of human nature. Is there a good side and bad side to all of us? Clearly, Dr. Jekyll and Mr. Hyde is an examination of the duality of human nature, as most clearly expressed in the revelation that Mr. Hyde is in fact Dr. Jekyll, only transformed into a personification of Jekyll's evil characteristics. Utterson's discovery of Jekyll's astounding work occurs in the final chapter of the novel, after Stevenson has laid the groundwork of evidence for the extreme duality inherent in human nature. We have already witnessed Hyde's powerfully vicious violence and have seen the contrasting kind, gentle, and honorable Dr. Jekyll. In approaching the novel's mystery, Utterson never imagines that Hyde and Jekyll are the same man, as he finds it impossible to reconcile their strikingly different behavior.