for you will heap burning coals on his head, and the LORD will reward you.
By this it appears that, however the scribes and Pharisees had corrupted the law, not only the commandment of loving our brethren, but even that of loving our enemies, was not only a new, but also an old commandment, an Old Testament commandment, though our Saviour has given it to us with the new enforcement of his own great example in loving us when we were enemies. Observe, 1.
Commenting on Proverbs 25:21-22
For thou shall heap coals of fire upon his head,.... Not to increase his punishment and damnation, the more aggravated by kindness shown him; but to bring him by such means to a sense of former injuries, and to shame for them, repentance of them, and love of the person injured, and carefulness for the future of doing him any further wrong; and the Lord...
For thou shalt heap coals of fire upon his head, and the LORD shall reward thee. (p) You will, as if by force, overcome him, in so much that his own conscience will move him to acknowledge the benefits, and his heart will be inflamed.