This teaching endorses what I have already stated that the Christian's enemies are to be pitied in that they are subjected to the wrath of God. Paul here introduces a quotation from Solomon. Prov 25, 21-22. Heaping coals of fire on the head, to my thought, implies conferring favors upon the enemy. Being enkindled by our kindness, he ultimately becomes displeased with him- self and more kindly disposed to us.
Coals here are benefits, or favors.
I do not think a Christian should desire punishment to fall upon his enemy, though such explanation of the sentence is not inapt. Be not overcome of evil, but overcome evil with good. Overcoming by force is equivalent to lending yourself to evil and wronging the enemy who wrongs you. But if you overcome him with good, he will be made righteous like you.