John Calvin Commentary Exodus 8:16

"And Jehovah said unto Moses, Say unto Aaron, Stretch out thy rod, and smite the dust of the earth, that is may become lice throughout all the land of Egypt." — Exodus 8:16 (ASV)

And the Lord said to Moses. In this instance again, as before, Aaron is commanded to act as Moses' subordinate in punishing the tyrant. This was more disgraceful than if Moses alone had been employed.

The nature of this third plague is very remarkable. God troubled Egypt not only with frogs but also with lice. For although the Hebrews are not entirely agreed about the כנם, kinim, they admit that these were little animals or insects that produced shame along with annoyance, even for the lowliest of people.

We see then how magnificently God trampled upon the pride of Egypt by inflicting a punishment full of insult and disgrace. Although it would have been painful to fall to a powerful and warlike enemy, it was far more grievous to be degradingly destroyed by lice. Nor can we doubt that God prepared such an army as this, primarily so that He might openly demonstrate how easily He can mockingly bring to nothing all earthly strength and power.

Surely, unless the Egyptians had been utterly foolish and irrational, this thought would have occurred to them: what would happen next if the Maker of heaven and earth were to apply His full power to their destruction, especially when they perceived themselves being worn down in this almost ridiculous contest with Him?

But let us learn from this history that all creatures are ready at God’s slightest command whenever He chooses to use them to punish His enemies; and again, that no animal is so lowly and contemptible that it lacks the power to cause harm when God employs it; and finally, that reprobates ultimately achieve this by their proud actions: namely, that they are, with the greatest disgrace, made to yield even to worms or to lice.