As punishment for the complaints of the Israelites, God sent poisonous serpents that bit and killed them. Moses prepared a serpent of bronze, and anyone who had been bitten looked at it and was cured. The Sages explain that, obviously, it was not the Israelites’ gazing at the snake that provided the cure, but rather their thoughts of repentance caused by their looking at it.

“Craft for yourself a fiery serpent, and place it upon a pole; it shall be that anyone who was bitten, will see it and live” (Numbers 21:8). Does a serpent kill, or does a serpent preserve life? This means that when the Jewish people turned their eyes upward and subjected their hearts to their Father in Heaven, they would be healed, but if not, they would deteriorate. (Mishna Rosh HaShana 3:8)