So I take it that "heaping hot coals on the head" as part of praying for a bad person, is a good thing?
Seems rather,well, ambiguous in the good department if you ask me. But it does allow one to pray with a clear conscience while knowing the old head of the despised one is getting some hot coals poured on it.
Actually, it causes them discomfort because they know they are wrong and that what you are doing is right. Human nature is evil, but we are imbued with a sense of God and right and wrong whether we follow our inner selves or not. The saying is meant to demonstrate this part of our nature and comes from Go Himself. The Bible contains all the wisdom and instructions for life that we need.
God Bless.