Gen 3:15, Jn 3:14-15, Gal 3:13, Col 2:15
In the Old Testament, the Israelites resented God and God caused them to be bitten by vipers to death. But those who saw the bronze serpent that Moses placed on the pole lived. (Num 21:8-9)
Num 21:8 And the Lord said unto Moses, Make thee a fiery serpent, and set it upon a pole: and it shall come to pass, that every one that is bitten, when he looketh upon it, shall live. 9 And Moses made a serpent of brass, and put it upon a pole, and it came to pass, that if a serpent had bitten any man, when he beheld the serpent of brass, he lived.
In the Old Testament it was foretold that Christ would die on the cross. (Genesis 3:15)
Genesis 3:15 And I will put enmity between thee and the woman, and between thy seed and her seed; it shall bruise thy head, and thou shalt bruise his heel.
Jesus paid for our sins by being lifted up like the brass serpent of Moses on the cross and dying. And He gave eternal life to those who believe in Him as the Christ. (John 3:14-15, Gal 3:13, Col 2:13-15)
John 3:14 And as Moses lifted up the serpent in the wilderness, even so must the Son of man be lifted up: 15 That whosoever believeth in him should not perish, but have eternal life.
Gal 3:13 Christ hath redeemed us from the curse of the law, being made a curse for us: for it is written, Cursed is every one that hangeth on a tree:
Col 2:13 And you, being dead in your sins and the uncircumcision of your flesh, hath he quickened together with him, having forgiven you all trespasses; 14 Blotting out the handwriting of ordinances that was against us, which was contrary to us, and took it out of the way, nailing it to his cross; 15 And having spoiled principalities and powers, he made a shew of them openly, triumphing over them in it.