Exodus 7:8

8.And the Lord spake. No wonder that Moses often repeats the same thing, because he wrote for persons of rude and dull minds. But it behooves us, lest we should be disgusted by his simple and popular style, diligently to examine how little we are inclined to be acute and earnest in our consideration of the works of God. No doubt there is here related what we have already heard respecting the change of the rod into a serpent, except that he now tells us that the miracle which had before been performed in the wilderness of Midian, and afterwards in Egypt, in the sight of the people, was likewise performed once more before Pharaoh. Moreover, we gather from hence that at the request of Pharaoh the servants of God had proved and testified their vocation; and therefore that his pertinacity was the less excusable, since he despised the power of God so manifestly shewn forth. For this is usual with unbelievers, to demand proofs of God’s power, which they may still discredit, — not that they professedly scorn God, but because their secret impiety urges them to seek after subterfuges. The message is disagreeable and full of what is annoying to the proud king; and because he does not dare directly to refuse God, he invents a plausible pretext for his refusal, by asking for a miracle; and when this is performed, he seeks still deeper lurking places, as we shall very soon perceive. Since, therefore, it was certain that he would not pay a willing obedience to the divine command, and would not yield before he had been miraculously convinced, God furnishes His servants with a notable and sure testimony of His power. Moreover, the change of the crook, or shepherd’s staff, into a serpent had this object, namely, that the mean and rustic guise of Moses should not be despised. For (since kings are wont to exalt themselves very highly) Pharaoh might have laughed at the audacity of Moses and Aaron, who, forgetful, as it seemed, of their condition, put themselves into conflict with the whole power of Egypt; but Pharaoh knew, although they were not to be dreaded for their splendid appearance, and had nothing magnificent about them, that they were still not destitute of sure and strong help, when he saw the serpent come forth from the rod. In a word, God bore witness that His power is hidden beneath the infirmity of His servants, so that at every season He might render formidable to the greatest monarchs those who otherwise are like earthen vessels. It is not clear to me why Aaron was commanded to cast down the rod rather than Moses, unless, perhaps, because God would designedly humble the pride of the arrogant king, when He did not deign to exert His power by the hand of His superior servant, but only employed the inferior one. Therefore, with reference to this ministration, the rod of God and of Moses is now called the rod of Aaron. Thus Paul boasts of his gospel, the office of preaching which he knew to be committed to him. (Romans 16:25, and 2 Timothy 2:8.)