A fiery flying serpent is a poisonous snake. "Fiery" refers to being poisonous and "flying" probably refers to their striking motion in an attempt to bite. The Book of Mormon, as in many other instances, teaches us as much about this Bible story as the Bible does. Numbers states that after the people had murmured again, the Lord sent serpents which bit them. Then the Lord said unto Moses, Make thee a fiery serpent, and set it upon a pole: and it shall come to pass, that every one that is bitten, when he looketh upon it, shall live. And Moses made a serpent of brass, and put it upon a pole, and it came to pass, that if a serpent had bitten any man, when he beheld the serpent of brass, he lived (Num 21:8-9).
John makes brief mention that the serpent raised by Moses represented the Messiah being lifted up on the cross (Jn 3:14). It is Alma who teaches us that there were many who perished, simply because they did not believe that it would heal them. He continues:
O my brethren, if ye could be healed by merely casting about your eyes that ye might be healed, would ye not behold quickly, or would ye rather harden your hearts in unbelief, and be slothful, that ye would not cast about your eyes, that ye might perish?
If so, wo shall come upon you; but if not so, then cast about your eyes and begin to believe in the Son of God, that he will come to redeem his people, and that he shall suffer and die to atone for their sins; and that he shall rise again from the dead, which shall bring to pass the resurrection, that all men shall stand before him, to be judged at the last and judgment day, according to their works. (Alma 33:21-2)
The imagery of Christ as a serpent continued long after the death of the Nephites. One of the ways in which the god, Quetzalcoatl, is represented is as a feathered serpent.
"Now, the strange fact is that the winged serpent, or the feathered serpent, plays a prominent part also in the religious concepts of the American Indians, and in their traditions. Among the ancient Mexicans, one of the divinities was known as 'the feathered' or 'plumed serpent,' Quetzalcoatl, which name corresponds to the 'flying serpent' of the Hebrews. Quetzalcoatl among the Mexicans was what the brazen serpent was to the Hebrews-the representative of the healing, life-giving power." (Reynolds and Sjodahl, Commentary on the Book of Mormon, vol. 1, p. 267)