The tribes had moved to an area where snakes began coming out of the rocks, biting the people and people were dying from the venom. God commanded Moses to make a brass image of the snake and raise it high above the camp, so that anyone, yes ANYONE, who even looked at the brass image and believed God would heal them, they were healed.
Now Bible teachers will tell you that the snake poison represents sin and the belief that God made a promise to heal the poison effect represents the efficacy of Jesus fulfilling God's Promise regarding our sins.
Here's the astonishing thing about the episode that points so strongly at catholiciism today being lots of things but not Christianity: just a few generations after the snake on the pole episode, the Hebrews were casting snakes and bowing to them for healing of everything from foot fungus to word wounds and common colds. The people had made an idol out of the episode, and God commanded them through the prophet/king to stop the idolatry. The parallel to the snake being idolized for manipulating God's Promises (idolatry) by the later generations is like unto the idolizing of Mary, with the same methodology and statuary veneration (idolatry).
If you would like to refute my accusation regarding the parallels between the Mariology idolatry and the brass snake idolatry, read the stories in The Torah and John 3. See what God's Spirit will say to you through His Word, the Word made flesh Who dwelt among us.
‘word wounds’ should read SWORD wounds. Old and arthritic fingers ...