John Calvin Commentary Romans 12:20

"But 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." — Romans 12:20 (ASV)

If therefore, etc. He now shows how we can truly fulfill the commands of not taking revenge and not repaying evil, even when we not only refrain from doing injury but also do good to those who have wronged us. For it is a kind of indirect retaliation when we withhold our kindness from those by whom we have been injured.

Understand that all acts of kindness are included under the words meat and drink. Therefore, whatever your ability may be, in whatever situation your enemy may need your wealth, your counsel, or your efforts, you ought to help him.

But he calls him our enemy, not one whom we regard with hatred, but one who harbors enmity towards us. And if they are to be helped in worldly matters, much less should their salvation be opposed by calling down vengeance on them.

You shall heap coals of fire, etc. Since we are not willing for our toil and labor to be lost, he shows what fruit will follow when we treat our enemies with acts of kindness. But some understand coals as the destruction that comes back upon the head of our enemy when we show kindness to someone unworthy and treat him differently than he deserves; for in this way his guilt is doubled. Others prefer to take this view: that when he sees himself so kindly treated, his mind is drawn to love us in return. I take a simpler view: that his mind will be turned to one side or another; for doubtless our enemy will either be softened by our benefits, or if he is so savage that nothing can tame him, he will yet be burned and tormented by the testimony of his own conscience on finding himself overwhelmed with our kindness.