「If your enemy is hungry, give him bread to eat;And if he is thirsty, give him water to drink; 25:22 For so you will heap coals of fire on his head,And the Lord will reward you.」
People at that time carried jars, jugs, and vegetable baskets on their heads. The only fire in the house was in a brazier. When the fire went out, they would go to the neighbor's house to borrow some charcoal. Kind neighbors would heap a lot of coals, but otherwise they would heap only a little. Then they would return home with the brazier on their heads. Paul was told that this act (verse 21) was like heaping coals on a cold brazier. (See Romans 12:20).