Exodus 7:22

And the magicians—did so with their inchantments— There was perhaps no great difficulty for the magicians to imitate this miracle; and, when all the water of the land was turned into blood, to make a change in some small quantity, sufficient to mock the credulity of Pharaoh's hardened heart. The true test of their power, and of that of their gods, would have been, to have purified by a word these waters, which the Omnipotence of Jehovah had thus terribly corrupted. But God, as an expositor observes, by permitting these deluded men thus far to succeed in their opposition, took occasion to render their impious folly more conspicuous; since, by permitting them to change the waters into blood, and putting it out of their power to restore them to their former purity; and by permitting them to produce frogs which they were not able to remove; he only put it in their power to increase those plagues upon themselves and their countrymen, at the same time that they demonstrated their own inability. See Bishop Kidder. If we consider that the Nile was not only the prime source of great plenty, but the great object of Egyptian honour and adoration; that their country was watered wholly by it; and that they gloried particularly in it; we shall see the striking propriety of this miracle, as well as the extreme severity of the punishment. See Plutarch de Isid. & Osir. There is nothing, says Plutarch, which the Egyptians have in greater veneration than the Nile. It is also to be observed, that the Egyptians, in ancient times, used to sacrifice annually, at the opening of the canals, a girl to the Nile, as a tribute paid to that river, for all the benefits received from it; and, therefore, "this turning its waters into blood," as Owen on Miracles remarks, "was a just and suitable punishment for such bloody cruelties." See Univ. Hist. vol. 1: p. 413.