Verse 20. The waters that were in the river were turned into blood - This was a plague justly inflicted upon the Egyptians; for Nilus 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 the creator. 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, Rev. xvi, 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.
Verse 22. And the magicians did so - By God's permission with their enchantments; and this served Pharaoh for an excuse not to set his heart to this also, (ver. 23,) and a poor excuse it was. Could they have turned the river of blood into water again, it had been something; then they had proved their power, and Pharaoh had been obliged to them as his benefactors.
Verse 25. Seven days were fulfilled - Before this plague was removed.