Bible Translation is the NKJV unless noted otherwise.
When we read in Paul's letter to the Romans, we come across an interesting statement.
Instead, if your enemy hungers, feed him; if he thirsts, give him a drink, for in so doing you will heap burning coals upon his head.
(Romans 12:20)
But what does it mean to "heap burning coals" upon someone's head? Does it have to do with increasing a person's condemnation before God? Or does it have to do with the person feeling shame? Or is it something else? And how can we be sure?
Although it might be tempting to read this idiom as if it referred to increasing the enemy's condemnation (based upon the context of Romans 12 and the typical association of burning coals with judgment), this is not what the idiom refers to. Rather, the idiom refers to what happens when one person makes another feel remorseful shame for their actions. They feel a burning shame like "burning coals" heaped up on their head.
How can we be sure?
First, we can go back to the source of the statement, which is certainly not Paul, but rather, the Proverbs.
If your enemy is hungry, give him bread to eat,
And if he is thirsty, give him water to drink,
For you are heaping coals of fire on his head,
And Yahweh will repay you.
(Proverbs 25:21-22)
Notice, that it is you who is heaping the coals in the verse, and not God. Everywhere else where burning coals are associated with God's wrath, it is God who is bringing them down on men. Also, if the coals of fire here had to do with God's retribution or punishment upon the enemy, we would expect the next phrase to be "And Yahweh will avenge you." But notice, that Yahweh does not "avenge you", but "repays" you. The verb root is "shalam" [שלם]. This verb root can sometimes refer to vengeance, but in such cases, the person being "repayed" - designated by the [ל] ("le") prefix on the pronoun - is the person who is receiving the vengeance and punishment. Here are a few examples:
כי עבדו־בם גם־המה גוים רבים ומלכים גדולים ושׁלמתי להם כפעלם וכמעשׂה ידיהם
(Jeremiah 25:14)
“A roaring sound from the city, a voice from the temple, the voice of Yahweh, repaying recompense to His enemies!
קול שׁאון מעיר קול מהיכל קול יהוה משׁלם גמול לאיביו
(Isaiah 66:6)
So if we were to understand the verb as taking vengeance here in Proverbs 25, it would mean that Yahweh takes his vengeance upon you, and not your enemy! This, of course, is an absurd interpretation. Rather, we can understand the meaning of "shalam" to be similar to how we read it here:
He who shows favour to the poor lends to Yahweh,
And He repays to him his deed.
(Proverbs 19:17)
Yahweh will repay a person for giving to the poor.
So also it is with the verse in discussion (in Proverbs 25); you are the one being repayed. And that is a good thing. Whatever you had given to your enemy - God will repay you. What an excellent promise for the believer.
We see this very principle laid out in the story of David and Saul, in 1Samuel 24. David has the perfect opportunity to kill Saul, the one who hates him, but instead, he uses the situation to defuse Saul's hatred for him.
And the men of Dawid said to him, “Behold, the day of which Yahweh said to you, ‘Behold, I am giving your enemy into your hand, and you shall do to him as it seems good to you!’ ” And Dawid arose and gently cut off a corner of Sha’ul’s robe.
(1Samuel 24:4)
After he cuts off a piece of his robe, he calls out to Saul, telling him about what he just did, and Saul replies:
And it came to be, when Dawid had ended speaking these words to Sha’ul, that Sha’ul said, “Is this your voice, my son Dawid?” So Sha’ul lifted up his voice and wept. And he said to Dawid, “You are more righteous than I, for you have rewarded me with good, whereas I have rewarded you with evil. And you have shown today how you have done good to me, for when Yahweh surrendered me into your hand you did not slay me. For if a man finds his enemy, shall he let him get away safely? And let Yahweh repay you with good for what you have done to me today.
(1Samuel 24:16 -19)
David heaped coals of fire on Saul's head by his actions, and Saul was made to feel remorseful.
Notice what Saul said:
"And let Yahweh repay you with good..."
And remember what it says in Proverbs 25:
"And Yahweh will repay you."
So then, the idiom "heaping burning coals" has nothing to do with divine vengeance in the Proverbs where it is found. (This is not to say that enemies will be punished by God for whatever they do to you. They most certainly will be punished if they do not repent.) Although there were some early writers who thought that the phrase had to do with adding to the enemy's condemnation, Jerome, a 4th century man with a good familiarity with Jewish idioms, had this to say:
For by so doing you shall "heap coals of fire upon his head", not by way of curse and condemnation, as most people think, but to chasten and bring him to repentance...
(Jerome, Against the Pelagians - Book 1 Ch.30)
But there is yet another reason that we can be sure that the idiom has to do with remorseful shame. The idiom occurs in another work of literature. This work, called 2 Esdras, is dated to the first or second century AD, and says the following:
Let not the sinner say that he has not sinned. For God shall burn coals of fire upon his head - he who says before the Lord God and his glory, "I have not sinned." Behold, the Lord knows all the works of men, their schemes, their thoughts, and their hearts:
(2 Esdras 16:53-54)
Although the verb is different (burn instead of heap), the meaning is still the same: God will make the person who says he has never sinned to feel utterly ashamed of himself, because he knows every act and intention of a man and will reveal everything to him on judgment day. It makes much less sense to say that the verse in 2 Esdras has to do with God bringing down divine wrath on someone just because they said that they have not sinned.
The goal of "heaping fire on someone's head" then, is to bring repentance and reconciliation, so that our enemies cease to even wish to be our enemies any longer. The author of the Didache (another early Jewish-Christian writing) likewise taught that showing compassion to our enemies has a restorative effect.
...But love those who hate you, and you shall not have an enemy.
(Didache 1:8)
Which should be no surprise, since God himself does the same!
Or do you despise the riches of his kindness and forbearance and patience, not knowing that the kindness of God is meant to lead you to repentance?
(Romans 2:4)
In summary - shame and remorse can bring reconciliation, which is the our goal for all who hate us. So we must overcome evil with good, and conquer malevolence with benevolence.