Why did God tell Moses to make a bronze serpent and put it on a pole? The children of Israel
complained about not having reached the Land of Canaan, their food, their water, and the manna.
Therefore, the Lord sent fiery serpents among the people, and the bites from the serpents caused many people to die. When the Israelites realized what they had done, they confessed their sin and asked Moses to pray for them. Then the Lord told Moses to make the bronze serpent, and whoever looked at it would be healed of his snake bite.
Then the Lord said to Moses, “Make a fiery serpent, and set it on a pole; and it shall be that everyone who is bitten, when he looks at it, shall live.” So Moses made a bronze serpent, and put it on a pole; and so it was, if a serpent had bitten anyone, when he looked at the bronze serpent, he lived (Numbers 21.8, 9).
Jesus explained to Nicodemus, how He Jesus, was like the serpent,
“And as Moses lifted up the serpent in the wilderness, even so must the Son of Man be lifted up, 15 that whoever believes in Him should not perish but have eternal life. For God so loved the world that He gave His only begotten Son, that whoever believes in Him should not perish but have everlasting life. For God did not send His Son into the world to condemn the world, but that the world through Him might be saved. He who believes in Him is not condemned; but he who does not believe is condemned already, because he has not believed in the name of the only begotten Son of God” (John 3.14–18).
As the serpent was lifted up, so Jesus would be lifted up, signifying His crucifixion, that is, He would be lifted up on a pole.
Jesus explained further why God sent Jesus into the world, to save the world, not condemn it, for the world was already condemned, even as the Israelites were already condemned, but the serpent saved them, and so Jesus would save people.
- Sermon: Christ in Numbers (grantspasschurchofchrist.com)