Bede

"For you will heap coals of fire on his head," etc. It does not speak of the burning of punishments; for wisdom would not teach that you should minister good to an enemy for the cause of his destruction; but the coals upon his head signify the ardor of charity in his heart. For sometimes, an enemy, overcome by frequent benefits, with the rigor of hatred softened, receives in his mind the warmth of charity, and turns from an enemy into a friend, and begins to reclaim the one whom he unjustly hated.

Commentary on Proverbs ↗