Exodus 10

In the eighth place locusts are mentioned. Some interpreters think that this sort of plague confutes the inconstancy of the human race, filled with dissent and discord. In another sense, the locusts can be interpreted as representing flittering mobility, like the pleasures of this world in a restless and skittish soul.

And the briefly recorded fact that the heart of Pharaoh experienced a kind of softening when he said, "But you shall not proceed far; you shall go a three days' journey and leave your wives behind," and whatever else he spoke when yielding before the marvelous works makes it clear that these signs had some effect even on him, though they did not entirely accomplish their object. Yet not even this would have happened if the idea held by most people about the words, "I will harden Pharaoh's heart," rightly represented what was wrought by him, that is, by God.

Even the locust, by divine grace, penetrates everywhere, and when it has filled the width of each region with its dense swarm, it first strikes without harm, and feeds on the barren land only after receiving the divine signal of permission. Indeed, just as we read in Exodus, it also acts as the celestial executor of righteous vengeance.

In the ninth plague, darkness fell. Either it means the blindness of their minds or that they should realize that the workings of the divine economy and of providence are most obscure. For God made darkness his hiding place. But they desired boldly and rashly to investigate it and, drawing one conclusion after another, fell into the dense and palpable darkness of ignorance.