At first glance, this verse might appear like some form of psychological revenge in order to guilt your enemy into saying, "I'm sorry."  The passage, though, seems to be referring to an ancient ritual of reconciliation.  Bible historians have found evidence of such a reconciliation in ancient Egypt.  For the people living in those early civilizations, fire was something extremely valuable.  Hot coals, used for cooking and heating, was a tool very neccessary for life.  The act of actually heaping fiery coals into somone's pot so that he or she could carry it back home on their heads, was an act of kindness and generosity.  Sharing your hot coals was an action viewed as life giving!  As Christians, you and I are not supposed to be passive.  God is calling us to actively engage in doing good even to our enemies!