Numbers 21 vs 8-9
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.
When the bronze snake was hung on the pole, the Isrealites didn’t know the fuller meaning Jesus Christ would bring to this event (see John 3:14-17)
And as Moses lifted up the serpent in the wilderness, even so must the Son of Man be lifted up, 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. Jesus explained that just as the Israelites were healed of their sickness of sin by looking at the snake that healed the people, but their belief that God could heal them. This belief was demonstrated by their obedience to God’s instructions. In the same way, we should continue to look to Christ (see Hebrews 12:2).