For many years I thought that the verse in the New Testament that is a quote of this one was wrong. It just did not line up with my understanding of grace. Then one day I was at a training course and the leader gave us all the true meaning of heaping coals on his head.
Proverbs 25:21-22
21 If your enemy is hungry, give him bread to eat; And if he is thirsty, give him water to drink; 22 For so you will heap coals of fire on his head, And the LORD will reward you.
Many people think that feeding your enemy or giving your enemy a drink this will really hurt him similar to if you had put hot coals on his head. This is a miss-understanding of scripture and it does not have the same meaning these days as we don’t live in the times when this was said.
In the time Solomon wrote this and it was quotes in the NT, there was a person in every village all night and tended a fire all night, making hot coals. This person each night early in the morning would load up all the coals into an urn and put it on his head and go from house to house and give each lady enough coals to start her fire.
So, when it talks about heaping coals of fire on his head, it is saying that by feeding your enemy and treating him with kindness, you might make him into a blessing for your community. One way is the soldiers that you have captured and fed, might go back to where they came from and talk them out of attacking you and your people again.
This verse also says if you treat your enemies with love, that the Father God will reward you for your efforts. God does not miss anything. Our Father in heaven looks at all that we do and He is not too busy to see every good thing that we do.