During their forty years in the wilderness, the Israelites provided a good illustration of faith in God. On one occasion they complained against God and Moses in the wilderness (Num. 21:4-9). God was displeased with their ingratitude and punished them with poisonous serpents. When they saw their predicament, they asked Moses to pray to God for their deliverance. God answered Moses' prayer by telling him to raise a brass serpent on a pole. He told Moses that anyone who was bitten need only to look at the brass serpent and he would live. Through faith in God's provision, all those who looked at it lived.
And as Moses lifted up the serpent in the wilderness, so must the Son of Man be lifted up, that whoever believes in him may have eternal life. For God so loved the world, that he gave his only Son, that whoever believes in him should not perish but have eternal life. —John 3:14-16
Jesus used this event in Israel's history to explain how he would provide eternal life through his death on the cross. All of us deserve God's eternal punishment for our sins. And yet God loved us and provided Jesus to die on the cross for our sins. This was the only way that each of us could be saved from the horrible punishment we deserve. God became man and lived on the earth. His name was Jesus, the perfect Son of God, who lived a perfect life and then willingly died on the cross for the sins of the world. Because he became a man, he understood the temptations we face. And because he is God, he could pay the overwhelming debt for the sins of the world.