But Pharaoh said, “Who is the LORD, that I should obey his voice and let Israel go? I do not know the LORD, and moreover, I will not let Israel go.”
2. And Pharaoh said, Who is the Lord? It is scarcely credible that there should be such madness in a mortal as, by thus wantonly scorning God, to fly, as it were, in the face of heaven! Quasi in coelum conspueret. — Lat.
Moses and Aaron, having delivered their message to the elders of Israel, with whom they found good acceptance, are now to deal with Pharaoh, to whom they come in peril of their lives - Moses particularly, who perhaps was out-lawed for killing the Egyptian forty years before, so that if any of the old courtiers should happen to remember that against him now it might cost him his head.
Commenting on Exodus 5:1-2
And Pharaoh said, who is the Lord,.... Jehovah, they made mention of, which, whether he took it for the name of a deity, or of a king, whose ambassadors they declared themselves to be, was a name he had never heard of before; and this being expressed and pronounced, shows that this name is not ineffable, or unlawful to be pronounced, as say the Jews...