Burning coals are mentioned several times in Scripture, usually referring to the literal red-hot coals of a fire (John 21:9). However, Proverbs 25:21–22 has a reference to burning coals that is probably not literal: “If your enemy is hungry, give him food to eat; if he is thirsty, give him water to drink. In doing this, you will heap burning coals on his head, and the Lord will reward you.” Paul quotes this passage again in Romans 12:20, and it is probable that neither passage is speaking of literal coals.
Paul’s choice of this metaphor is explained by the context of Romans 12. He is addressing the proper response of a Christian when treated wrongly. Verse 21 explains the idea of heaping burning coals on someone by saying, “Do not be overcome by evil, but overcome evil with good.” Anyone can return evil for evil. But when a Christian does so, the watching world sees nothing different about our lives. It is not even clear who is right and who is wrong when we respond in kind the one who wronged us. But, when we follow Jesus’ instruction to love our enemies (Matthew 5:43–44) and return good for evil, the contrast is stark. Our kind and gentle reaction to hatred spotlights the depravity of the one who treated us poorly and leaves the hurtful person alone in his or her hatefulness. Nothing pricks the conscience of a hateful person like a soft, forgiving spirit in the one he has wronged (Proverbs 15:1). The “burning coals” that are heaped on his head could be a reference to the burning shame he will feel as his conscience works upon him.
Burning coals in the Bible also symbolize judgment (Psalm 140:10) and spiritual purification (Isaiah 6:6; Leviticus 16:12). God is compared often to fire (Deuteronomy 4:24; Hebrews 12:9) and is described in terms that relate to fire’s heat, brightness, and power (Exodus 24:17; Isaiah 34:14; Psalm 18:8). So another understanding of “burning coals” in Proverbs 25:22 is that our right response to those who do us harm allows God’s own power and judgment to fall upon that person. We must “leave room for God’s wrath” (Romans 12:19) and wait for the vengeance God brings in His own time. When we relinquish to God our right to take revenge, we show faith in His justice. God will bring conviction upon the sinning heart. Responding the way Jesus did to His enemies (Luke 23:34) allows the “burning coals” of God’s righteousness and justice to operate within the soul of that person and hopefully bring him to repentance (2 Peter 3:9).