Gregory of Nazianzus

So in the case of one of us, if he leans to either side, whether from vice or ignorance, no slight danger of a fall into sin from vice or ignorance, no slight danger of a fall into sin is incurred, both for himself and those who are led by him. But we must really walk in the king’s highway and take care not to turn aside from it either to the right hand or to the left, as the Proverbs say. For such is the case with our passions, and such in this matter is the straight path of the good shepherd, if he is to know properly the souls of his flock, and to guide them according to the methods of a pastoral care which is right and just and be worthy of our true Shepherd.

That brazen serpent was hung up as a remedy for the biting serpents, not as a type of him that suffered for us but as a contrast. It saved those that looked upon it, not because they believed it to live but because it was killed, and killed with it were the powers that were subject to it, being destroyed as it deserved. And what is the fitting epitaph for it from us? “O death, where is your sting? O grave, where is your victory?” You are overthrown by the cross. You are slain by him who is the giver of life. You are without breath, dead, without motion, even though you keep the form of a serpent lifted up high on a pole.