Question: "Why is a bronze serpent used to save the Israelites in Numbers 21:8-9?"
Answer: Throughout the wilderness wanderings of the Israelites, God was constantly teaching them things about Himself and about their own sinfulness. He brought them into the wilderness, to the same mountain where He revealed Himself to Moses, so that He could instruct them in what He required of them. Shortly after the amazing events at Mt. Sinai, God brought them to the border of the Promised Land, but when the people heard the reports from the spies, their faith failed. They said that God could not overcome the giants in the land. As a result of this unbelief, God sent them into the wilderness to wander until that generation died out (Numbers 14:28-34).
In Numbers 21, the people again got discouraged, and in their unbelief they murmured against Moses for bringing them into the wilderness. They had already forgotten that it was their own sin that caused them to be there, and they tried to blame Moses for it. As a judgment against the people for their sin, God sent poisonous serpents into the camp, and people began to die. This showed the people that they were the ones in sin, and they came to Moses to confess that sin and ask for God's mercy. When Moses prayed for the people, God instructed him to make a bronze serpent and put it on a pole so the people could be healed (Numbers 21:5-7).
God was teaching the people something about faith. It is totally illogical to think that looking at a bronze image could heal anyone from snakebite, but that is exactly what God told them to do. It took an act of faith in God's plan for anyone to be healed, and the serpent on the stick was a reminder of their sin which brought about their suffering. There is no connection between this serpent and the serpent which Satan spoke through in the Garden of Eden. This serpent was symbolic of the serpents God used to chastise the people for their unbelief.
A couple of additional lessons are taught in the Bible regarding this bronze serpent. The people did get healed when they looked at the serpent, and the image was kept for many years. Many years later, when the Israelites were in the Promised Land, the serpent became an object of worship (2 Kings 18:4). This shows how easy it is for us to take the things of God and twist them into idolatry. We must never worship the tools or the people God chooses to use, but always bring the honor and glory to God alone.
The next reference we find in the Bible to this serpent is in John 3:14. Jesus indicated that this bronze serpent was a foreshadowing of Him. The serpent, a symbol of sin and judgment, was lifted up from the earth and put on a tree, which was a symbol of a curse (Galatians 3:13). The serpent lifted up and cursed symbolized Jesus, who takes away sin from everyone who would look to Him in faith, just like the Israelites had to look to the upraised symbol in the wilderness. Paul is reminding the Galatians that Jesus became a curse for us, although He was blameless and sinless—the spotless Lamb of God. “God made him who had no sin to be sin for us, so that in him we might become the righteousness of God” (2 Corinthians 5:21).