From Mount Hor they set out by the way to the Red Sea, to go around the land of Edom; but the people became impatient on the way. The people spoke against God and against Moses, "Why have you brought us up out of Egypt to die in the wilderness? For there is no food and no water, and we detest this miserable food." Then the Lord sent poisonous serpents among the people, and they bit the people, so that many Israelites died. The people came to Moses and said, "We have sinned by speaking against the Lord and against you; pray to the Lord to take away the serpents from us." So Moses prayed for the people. And the Lord said to Moses, "Make a poisonous serpent, and set it on a pole; and everyone who is bitten shall look at it and live." So Moses made a serpent of bronze, and put it upon a pole; and whenever a serpent bit someone, that person would look at the serpent of bronze and live.
Again he said to them, "I am going away, and you will search for me, but you will die in your sin. Where I am going, you cannot come." Then the Jews said, "Is he going to kill himself? Is that what he means by saying, "Where I am going, you cannot come"?" He said to them, "You are from below, I am from above; you are of this world, I am not of this world. I told you that you would die in your sins, for you will die in your sins unless you believe that I am he." They said to him, "Who are you?" Jesus said to them, "Why do I speak to you at all? I have much to say about you and much to condemn; but the one who sent me is true, and I declare to the world what I have heard from him." They did not understand that he was speaking to them about the Father. So Jesus said, "When you have lifted up the Son of Man, then you will realize that I am he, and that I do nothing on my own, but I speak these things as the Father instructed me. And the one who sent me is with me; he has not left me alone, for I always do what is pleasing to him." As he was saying these things, many believed in him.
The symbol of Israel's sin, the serpent that with its poisonous bite, is changed into an instrument of salvation. Moses made a bronze serpent and mounted it on a pole, so that all who look upon it admitting their sin and regretting their offense were cured by the Lord. Acknowledgment of sin purifies the mind and heart, exposing all excuses and calling evil by its proper name "sin" i.e. an offence against the God who guides our lives. The people come to a new outlook when they admit that sin brings sorrow and death, that their grumbling is destructive, and that their contempt for the Manna provoked God's anger. This bronze serpent has a somewhat murky history. Long before Moses cast this figure in copper, the serpent was a popular figurine in Canaanite fertility rituals. It was a serpent that symbolized the devil in Genesis 3. Perhaps it was because of this pagan background that Moses' bronze serpent later became an object of false worship and was destroyed as an idol by King Hezekiah (2 Kgs 18:4).
Paradoxically the early church recognized in this symbol a sign of Jesus on the cross. Saint Paul wrote: "For our sake God made the sinless one to be sin, so that in him we might become the very holiness of God" (2 Cor 5:21). In the goodness, compassion and forgiveness of Jesus we recognize by contrast our own violent and harsh attitudes. The very image of Jesus on the cross shows the effects of human violence but also reveals "the kindness and love of God our Saviour" (Tit 3:4). The "miraculous interchange" of which the liturgy speaks is that while Jesus conforms to us externally (adopting our humanity), we are enabled to conform to him internally, becoming children of God. His goodness forces the poison of our sinfulness out of our system, by his enduring with love the violence of the crucifixion, and through his act of loving self-surrender, we come to belong like Jesus to the Father who is above all.