14–15. As fire consumes the forest, and as the flame sets the mountains ablaze, so do Thou pursue them, etc. This is for all for good, or at least for the wicked in a bad sense, so that others, corrected by their example, may be filled with shame, as follows. How, then, does the fire consume the forest, or the flame the mountains? Is it different from firewood or chaff? Perhaps he wants to say that it is not with them as with gold and silver, which the fire tests and does not consume, while it does consume the firewood and the forests. Second, when fire burns up the forest and the mountains, it does not do so in a useful way, nor by men’s design, as does the fire which burns up wood and grass for cooking or heating. So the Jews are kindled with an altogether destructive fire of zeal that does no one any good but only brings about their destruction and ruin. So hell burns too. But the fire of the spirit does not burn up in this way. It burns off sins and evil from the soul, while preserving and saving the soul itself.
Luther’s works, vol. 11: First Lectures 2