What is the difference between proverb and idiom?
A proverb tells a moral lesson.
"A stitch in time saves nine."
"Early to bed, early to rise, makes a man healthy, wealthy, and wise."

"Keep your eyes wide open before marriage, half shut afterwards."

An idiom is a phrase that has a different meaning than if you looked up the individual words in a dictionary.
His words cut me to the quick. So I told him never to darken my door again.
Since he was three sheets to the wind, I'm reconsidering. You know the old proverb: "To err is human, to forgive divine."