The people spoke out against God and Moses, 'Why did you take us out of Egypt to die in the desert? There is no bread and no water! We are getting disgusted with this insubstantial food.' [They tired of the manna from God, calling it "wasteless." In other words, they craved sensation, and began to break the Law.]

God sent poisonous [literally: fiery] snakes against the people, and when they [tempting serpents of Eden] began biting the people, a number of Israelites died.

The people came to Moses and said, 'We have sinned by speaking against God and you. Pray to God, and have Him take the snakes away from us.'

God [Iod-Havah Elohai (Binah)] said to Moses, 'Make yourself [the image of] a snake, and place it on a pole. Everyone who is bitten shall look at it and live.'

Moses made a brazen [Hebrew nechosheth: brass] snake [Hebrew nachash] and placed it on a high pole. Whenever a snake bit a man, he would gaze at the brazen snake and live. - Quoted from Numbers 21

In synthesis, there are two forms of "serpents:"

1. The tempting serpents of Eden who tempt through sensation; those who fall into temptation are bitten, suffer, and "die" [spiritually], or in other words, are cast out of Eden.
2. The healing serpent of brass (or brazen serpent), made by raising up an image upon a pole (the spinal column). Compare to Moses facing the Pharoah, and Moses striking the rock with his staff.

Brass is made by combing two metals: copper (feminine) and tin (masculine). This story hides the secret of Alchemy: how to purify base metals and make them pure by raising a serpent (kundalini, or transmuted sexual energy) upon a staff (the spine).