John Calvin Commentary Exodus 7:20

"And Moses and Aaron did so, as Jehovah commanded; and he lifted up the rod, and smote the waters that were in the river, in the sight of Pharaoh, and in the sight of his servants; and all the waters that were in the river were turned to blood." — Exodus 7:20 (ASV)

And Moses and Aaron did so. He repeats that what God threatened concerning the death of the fish, and the stinking of the Nile, actually took place, so that he might aggravate the sin of the king, who was unaffected by the manifold power of God. Still, he immediately adds that his counsellors witnessed it also. From this we may conjecture that the same infatuation had pervaded the whole court.

It was also proper that such a memorable circumstance should not only be known generally, but that its author should be seen by many eyes. But it was a sign of the reprobation of the whole nation that there was none in all that multitude who labored to correct the folly of the king.

From this it also appears that God confounds the wisdom of the world, for there was no nation which gloried more in its universal knowledge, even as Isaiah reproaches them for their boast (Isaiah 19:11). But we see in how shameful a manner, on the one hand proud, and on the other amazed, they displayed not a single spark of sound intelligence.