When the people of Israel sinned in Numbers 21 -- complaining against the Lord and against His servant Moses -- God sends fiery serpents into their midst, "and much people died." (21.6). And while God sent the fiery serpents, he also provided the remedy, and Moses was commanded to place a replica of the serpent on a pole, and hoist the pole, and those who saw the serpent replica lived.
Christ explicitly compares Himself to the serpent. It's important that we avoid making the crucifixion pretty. It's easy to do this, because we want to avoid the sheer horror of the scene. Our Lord was crucified at a place where Roman soldiers routinely killed people for crimes as little as theft. There were probably wild dogs there that fed off of the flesh of criminals who died and whose bodies happened to get left on the ground. It was hot. It was muggy. There would be insects. It was not nice.
But the point of Numbers 21 is that Christ says He is like the serpent. The serpent is the occasion for the sin of Adam, and the serpent is never an attractive figure. How is Christ like the serpent?
The clue to answering this question is found in II Cor. 5.20-21: "Now then we are ambassadors for Christ, as though God did beseech you by us: we pray you in Christ's stead, be ye reconciled to God. For he hath made him to be sin for us, who knew no sin; that we might be made the righteousness of God in him." Christ was made sin for us. Christ was made a serpent for us. Christ was made the evil that we are, in order to free us.