Adam Clarke on Job 1:16

The fire of God is fallen - Though the fire of God may mean a great, a tremendous fire, yet it is most natural to suppose lightning is meant; for as thunder was considered to be the voice of God, so lightning was the fire of God. And as the prince of the power of the air was permitted now to arm himself with this dreadful artillery of heaven, he might easily direct the zigzag lightning to every part of the fields where the sheep were feeding, and so destroy the whole in a moment.