To the contrary, “if your enemy is hungry, feed him; if he is thirsty, give him something to drink; for by so doing you will heap burning coals on his head.” (ESV)
We have learned in this section of Romans that God has a plan for us in how to deal with those who mistreat us. We are not to take vengeance upon our enemies. We are to leave vengeance in the Lord's hands. This is difficult for us. This is not how the world operates. We are not of the world so our actions should reflect that we have a changed heart.
While we know that we should not retaliate against our enemy if he has done us wrong, how should we treat our enemy when they are not acting aggressively towards us. Suppose that in the course of life we see that our enemy is experiencing hunger or thirst. Should we ignore them? It would be easy to do so. After all, we know that they do not deserve to be treated fairly.
Paul says that we are to feed our enemy when they are hungry and give our enemy something to drink if they are hungry. This is completely counter-cultural to our understanding. We have to realize that God has a purpose in mind when he gives us instruction. God looks at this person as one whom he has died for. We need to gain the Lord's perspective.
As for the burning coals, Dr. John MacArthur writes: "Refers to an ancient Egyptian custom in which a person who wanted to show public contrition carried a pan of burning coals on his head. The coals represented the burning pain of his shame and guilt. When believers lovingly help their enemies, it should bring shame to such people for their hate and animosity. (MacArthur Online Study Bible)"
Any time I wanted to hate another person my mother would always tell me, "Remember, that is someone Jesus died for." Timely advice. Let's all heed it.