Exodus 7:12

12.For they cast down every man. The number of the magicians is not expressed; and although Paul names two, Jannes and Jambres, (86) (2 Timothy 3:8,) it is probable that they were not the only ones, but the chief, and, as it were, the ringleaders. But I will not dispute this questionable point. The admonition of Paul is more to the purpose, that “as Jannes and Jambres withstood Moses,” so also there should always be false teachers, who would oppose Christ’s true ministers, and indeed should “wax worse and worse.” (Verse 13.) It is an awful fact that the reins were so given to these magicians, that they contended with Moses in almost an equal contest. But the ingratitude of the world is worthy of bearing the same punishment of blindness. God elsewhere testifies that when He permits false prophets to work miracles to deceive, it is to prove men’s hearts. (Deuteronomy 13:3.) And truly, unless our own hypocrisy were like a veil to take away the distinction between black and white, Satan would avail nothing by such arts and deceptions; but we ourselves, as if devoted to destruction, willingly cast ourselves into his nets; but especially against the reprobate, who obstinately seek for occasions of error, God casts this last thunderbolt, namely, He gives efficacy to the delusion, and so deprives them of their senses at the same time, that they do not guard themselves from manifest destruction. Many indeed would excuse Pharaoh, because, being deceived by his magicians, he did not disentangle himself from the error which he could not escape; for what could he do when he saw the contest equally maintained? But it must be thoroughly understood that none are so hurried away except those whom God would resist; especially the spirit of confusion and mental blindness seizes on those who have been obstinate in their wickedness. Nor must the mark of distinction be overlooked, that the rod of Moses swallowed up the rods of the magicians. How then was it that Pharaoh did not perceive Moses to be victorious? how was it that he rather turned aside to his own impostors? how was it, in fine, that he did not acknowledge God’s servant who had been superior in the contest, except that the wicked maliciously close their eyes against the manifested power of God? Whosoever will aim at the right mark shall certainly never be destitute of God as his guide. Therefore blame is justly thrown upon Pharaoh, because through the hardness of his heart he would not attend. Too frivolous is that cavil which the Papists advance, that the serpent is called the rod of Moses, as the bread transubstantiated into the body of Christ retains the name of bread; (87) for they unskillfully confound two altogether different things; because, in the mystery of the Lord’s Supper, the analogy between the sign and the thing signified always remains; in this miracle the case is entirely otherwise. Again, because the change was only temporary, Moses properly called that a rod to which its previous form was presently to be restored. Besides, in comparing the true serpent with the fictitious ones, he was unwilling to make a difference in names. But, to pass all this over, the Papists will prevail nothing, until they have shewn that the bread is transubstantiated into the body. (88) Nay, what they foolishly wrest against us, we may retort upon them, namely, that the bread is called the body of Christ although it remains bread, just as the serpent which then appeared is called the rod.

The subject is somewhat more fully discussed by C. himself —Institutes, Book 4., ch. 17. 15. — C. Soc. Transl. , Vol. 3, pp. 402, 403.