Fiery serpents means in the bible: Flame-like markings on snakes or bites that cause acute inflammation Num. 21:6. These were sent by the Lord upon Israel’s children to “straiten” them. He also prepared a way for those who had been bitten to be healed. Moses held up the serpent of brass before them as a symbol that Jesus was being raised from the dead John 3:14-15. This is also confirmed by the latter-day revelation 1 Ne. 17:41; 2 Ne. 25:20. Also see Serpent brazen.
(in Bible Dictionary)