John Calvin on Exodus 8:15

15. Blot when Pharaoh saw. Hence it appears that the wretched tyrant, like a winding serpent, twisted and turned his mind to crooked counsels; for when he was trembling beneath the present feeling of God’s power, he dared not obstinately resist any longer; he only sought a little breathing time; now, being freed from fear, he returns to his former contumacy. But this is a sign of a perverse and crooked disposition, not to submit willingly, but to pay only a temporary deference, when necessity is more than usually urgent. God foreknew, and had foretold to Moses, that this perfidy was hidden in the recesses of his heart; but he was willing to bring it to light, and therefore remitted the punishment; and hence was the opportunity for dissembling.

Exodus 8:16-19

16. And the Lord said unto Moses, Say unto Aaron, Stretch out thy rod, and smite the dust of the land, that it may become lice throughout all the land of Egypt.

16. Tunc dixit Jehova ad Mosen, Loquere ad Aharon, Extende virgam tuam, et percute pulverem terrae, ut sit in pediculos per totam terram Aegypti.

17. And they did so: for Aaron stretched out his hand with his rod, and smote the dust of the earth, and it became lice in man and in beast: all the dust of the land became lice throughout all the land of Egypt.

17. Et fecerunt sic: et extendit Aharon manum suam cum virga sua, et percussit pulverem terrae: ut fuit in pediculos in homine et jumento, totus pulvis terrae fuit in pediculos per universam terram Aegypti.

18. And the magicians did so with their enchantments to bring forth lice, but they could not: so there were lice upon man and upon beast.

18. Et sic fecerunt magi incantationibus suis ut producerent pediculos: sed non potuerunt.

19. Then the magicians said unto Pharaoh, This is the finger of God: and Pharaoh’s heart was hardened, and he hearkened not unto them; as the Lord had said.

19. Tunc dixerunt magi ad Pharaonem, Digitus Dei est hic. Et roboratum fuit cor Pharaonis, nec audivit eos, sicut loquutus erat Jehova.