The flame setteth the mountains on fire - This may refer to the burning of the straw and chaff, after the grain was threshed and winnowed. And as their threshing-floors were situated often on the hills or mountains, to take the advantage of the wind, the setting the mountains on fire may refer to the burning of the chaff, etc., in those places. Let them be like stubble driven away by the wind, and burnt by the fire.
As the fire burneth a wood - The same idea is here presented under another form. No image of desolation is more fearful than that of fire raging in a forest; or of fire on the mountains. As trees and shrubs and grass fall before such a flame, so the prayer is, that they who had combined against the people of God might be swept away by his just displeasure.