Heap coals of fire on his head (Proverbs 25:22)

bible verse

“In doing this, you will heap burning coals on his head, and the Lord will reward you.” (Proverbs 25:22)
“If your enemy is hungry, feed him; if he is thirsty, give him something to drink. In doing this, you will heap burning coals on his head.” (Romans 12:20)

meaning

This idiom refers to the situation when you act friendly towards an enemy.

origin and application

This phrase first appears in Proverbs which is later quoted by Paul the apostle in the Book of Romans. Paul asks us to love our enemy and overcome evil with good. In this way, we are heaping coals on his head.
There are several interpretations regarding the origin of this idiom. Some argue that the origin comes from an ancient tradition in Egypt, where criminals repented for their sins by heaping coals on their heads.
Others argue that the ancient nomadic people relied on fire for their work. If coals are extinguished in the morning, people are forced to beg for coals from their neighbours to keep them warm. Ancient people carry a bowlful of coal on the top of their head, hence the saying, “heaping coals on their heads”.