8Bear fruits worthy of repentance. He will baptize you with the Holy Spirit and fire. We think of the desert as barren, but it includes a good deal of vegetation that can burn fiercely.
High winds cause such fires to move quickly.
Snakes and other desert creatures try to move even more quickly to escape the flames. Such a fire would indeed inspire terror in such creatures, some of whom would die in the flames. Others would find their food supply destroyed. The desert, always challenging, is even less hospitable after such a fire. John likens the people who have come to be baptized to vipers who flee before the fire.