Bitten by a serpent

When the people murmered against G-d and Moses, G-d brought judgement on the peoples sin by serpents biting them, causing death. G-d in mercy also provided a way of escape by commanding Moses to make a fiery serpent and put it on a pole. Numbers 21:9 "And Moses made a serpent of brass, and put it upon a pole, and it came to pass that if a serpent had bitten any man, when he beheld the serpent of brass, he lived."

The serpent is a picture of Satan, the serpent's bite  is a picture of sin, the brass serpent is a picture of sin judged. This picture of sin judged by G-d is fulfilled in the New Covenant "And as Moses lifted up the serpent in the wilderness, even so must the Son of man be lifted up" John 3:14 When the Son of Man was lifted up on a tree,just like the brass serpent, it was for G-d's judgement of our sins. The Messiah was lifted up on the tree so that who ever looks on Messiah Yeshua will have their transgressions taken away by the Blood and live eternally with G-d.