Exodus 7:20 - Joseph Benson’s Commentary on the Old and New Testaments

The waters in the river were turned into blood This was a plague justly inflicted on the Egyptians; for the river of Egypt was their idol; they and their land had so much benefit by that creature, that they served and worshipped it more than their Creator. In ancient times they annually even sacrificed a girl to it, at the opening of the canals, Univ. Hist., vol. 1. p. 413. Also they had stained the river with the blood of the Hebrew children, and now God made that river all bloody; thus he gave them blood to drink, for they were worthy, Revelation 16:6. See the power of God! Every creature is that to us which he makes it to be, water or blood. See the mutability of all things under the sun, and what changes we may meet with in them. That which is water to-day may be blood to- morrow; what is always vain may soon become vexatious. And see what mischievous work sin makes! It is sin that turns our waters into blood. All the waters It seems the word all here, and in the foregoing verse, is either to be understood in a limited sense, as it frequently is in Scripture, meaning not all in the strictest sense, but only a very great part; or else that although Moses's commission extended to all the waters in Egypt, yet it was only executed upon the river Nile: because we read that the magicians did the same thing; but if Moses had turned all the waters into blood, as some scoffers have, with great raillery and triumph, observed, how could the magicians do the same, there being, on this supposition, no water for them upon which to make the trial.