Num 21:6

“And that He might increase in them this fear, immediately, by the mouth of offence, the rod of His chastisement was revealed, and after the offence the Chastiser gave them no respite, because their servitude was not worthy of His longsuffering. Above their head the rod of justice hung continually, and immediately they committed sin they were chastened, and at the time of their offence they were beaten, and at the entrance of the path of their sins they forthwith received rebuke; for longsuffering teacheth the foolish servant contempt, and in order that that stupid nation, which in the manner of an evil-doing servant, sat in the house of God, might not [learn] contempt, the Chastiser took away longsuffering, especially when they went forth from Egypt. And we must also understand the object of that swift punishment in another way, and that there was not longsuffering as regardeth the correction of their sins; for God the Teacher took the people, like a child, from Egypt their nurse, that He might deliver unto them the doctrine of His knowledge, and might teach them the instruction of His wisdom. But the people, in their ignorance, when instruction had been delivered unto them, forgot it, and they never kept in remembrance the meditation of the commandments of God, and they were frequently punished with severity, so that, if it were only through fear of chastisement, they might lay hold upon the remembrance of instruction. The man who gathered sticks on the Sabbath day was stoned by all the congregation; and the earth opened and swallowed up others who were called by Moses, and who scorned him and came not; and fire went forth suddenly, and burnt up the bodies of others who thought lightly of his priestly office, and who sought honour for themselves; and others, who in the guise of paying honour, brought strange fire out of season, were burnt up by a tongue of fire which went forth from the tabernacle, and they perished; and others, because they asked for flesh and rejected the bread of angels, were tortured by the indigestion which came upon them; and others who went astray as concerning the calf, were pierced through by the swords of the Levites; and others, who were the cause of the revolt at the waters of trial were set apart for destruction; and others who murmured against the Lord perished by fiendish snakes; and likewise they all, because they strove against going into the land of promise, came to an end and were destroyed in the wilderness. To these offences, then, these punishments were united, and together with each act of wickedness a punishment straightway sprang up by its side, so that evil deeds might be suppressed by stripes, and sins by vengeance, and so that the people might be like a child who feareth the teacher who giveth him instruction, and that it might tremble before the Judge who would beat them like a wrongdoing slave.”

“The wounds caused by the fiery serpent are the poisonous enticements of the vices, which afflict the soul and bring about its spiritual death. The people were murmuring against the Lord. They were stricken by the serpents' bites. This provides an excellent instance of how one may recognize from the results of an external scourge what a great calamity a person might suffer inwardly by murmuring. In the raising up of the bronze serpent (when those who were stricken beheld it, they were cured) is prefigured our Redeemer's suffering on the cross, for only by faith in him is the kingdom of death and sin overcome. The sins which drag down soul and body to destruction at the same time are appropriately represented by the serpents, not only because they were fiery and poisonous [and] artful at bringing about death but also because our first parents were led into sin by a serpent, and from being immortal they became mortal by sinning. The Lord is aptly made known by the bronze serpent, since he came in the likeness of sinful flesh. Just as the bronze serpent had the likeness of a fiery serpent but had absolutely none of the strength of harmful poison in its members—rather by being lifted up it cured those who had been stricken by the [live] serpents—so the Redeemer of the human race did not merely clothe himself in sinful flesh but entered bodily into the likeness of sinful flesh, in order that by suffering death on the cross in [this likeness] he might free those who believed in him from all sin and even from death itself.”