That's under debate :
Have you ever wondered why is a snake, which is a symbol of destruction[
4] used ironically as a symbol of healing? Well, the answer lies deep sown in history when Moses, around 1400 BC, used the bronze serpent erected on the pole to cure the people who were bitten by snakes.[
5] The other reasons why serpent has been used is the shedding of the skin that indicated longevity and immortality
Symbols