Romans 12:20

But [instead of avenging] if thine enemy hunger, feed him; if he thirst, give him to drink: for in so doing thou shalt heap coals of fire upon his head. [Quoted from Proverbs 25:21-22 LXX., where the words, "And Jehovah will reward thee," are added. Simply to forbear from avenging is only half a victory. The full conquest is to return good for evil (Luke 6:27-30). In feeding enemies we are like God, who daily feeds sinners, and the conduct of God is our law (Matthew 5:44-48). Heaping coals of fire is a figure derived from the crucible, where they were heaped upon the hard metal till it softened and melted. Kindness is not utterly lost on beasts, but with man it ought always to prevail, for it heaps coals upon the head, or seat of intelligence, filling the mind with the vehement pangs and pains of conscience, the torments of shame, remorse and self-reproach. The most effectual way of subduing an enemy is by the unbearable punishment of unfailing kindness--it is God's way. "The logic of kindness," says Johnson, "is more powerful than the logic of argument." The same thought is now repeated by the apostle without a figure.]