Notes on the Bible, by Albert Barnes, [1834], at sacred-texts.com
With this chapter begins the series of miracles which resulted in the deliverance of Israel. The first miracle was performed to remove the first obstacle, namely, the reluctance of Moses, conscious of his own weakness, and of the enormous power with which he would have to contend.
A rod - The word seems to denote the long staff which on Egyptian monuments is borne by men in positions of authority. It was usually made of acacia wood.
A serpent - This miracle had a meaning which Moses could not mistake. The serpent was probably the basilisk or Uraeus, the Cobra. This was the symbol of royal and divine power on the diadem of every Pharaoh. The conversion of the rod was not merely a portent, it was a sign, at once a pledge and representation of victory over the king and gods of Egypt!
Leprous - The instantaneous production and cure of the most malignant and subtle disease known to the Israelites was a sign of their danger if they resisted the command, and of their deliverance if they obeyed it. The infliction and cure were always regarded as special proofs of a divine intervention.
Eloquent - See the margin. The double expression "slow of speech (Eze 3:5 margin) and of a slow tongue" seems to imply a difficulty both in finding words and in giving them utterance, a very natural result of so long a period of a shepherd's life, passed in a foreign land.
Since thou hast spoken - This expression seems to imply that some short time had intervened between this address and the first communication of the divine purpose to Moses.
Compare with this our Lord's promise to His Apostles; Mat 10:19; Mar 13:11.
And he said - The reluctance of Moses is in accordance with the inner law of man's spiritual development, and specially with his own character; but, under the circumstances, it indicated a weakness of faith.
Anger - The words of Moses Exo 4:13 indicated more than a consciousness of infirmity; somewhat of vehemence and stubbornness.
Aaron - This is the first mention of Aaron. The words "he can speak well," probably imply that Aaron had both the power and will to speak. Aaron is here called "the Levite," with reference, it may be, to the future consecration of this tribe.
He cometh forth - i. e. is on the eve of setting forth. Not that Aaron was already on the way, but that he had the intention of going to his brother, probably because the enemies of Moses were now dead. See Exo 4:19.
Thou shalt speak - Moses thus retains his position as "mediator;" the word comes to him first, he transmits it to his brother.
Instead of a mouth - We may bear in mind Aaron's unbroken habitude of speaking Hebrew and his probable familiarity with Egyptian.
Instead of God - The word "God" is used of persons who represent the Deity, as kings or judges, and it is understood in this sense here: "Thou shalt be to him a master."
An ass - Literally, "the ass," which, according to Hebrew idiom, means that he set them upon asses. This is the first notice of other sons besides Gershom.
The rod of God - The staff of Moses was consecrated by the miracle Exo 4:2 and became "the rod of God."
I will harden - Calamities which do not subdue the heart harden it. In the case of Pharaoh, the hardening was at once a righteous judgment, and a natural result of a long series of oppressions and cruelties.
My firstborn - The expression would be perfectly intelligible to Pharaoh, whose official designation was "son of Ra." In numberless inscriptions the Pharaohs are styled "own sons" or "beloved sons" of the deity. It is here applied for the first time to Israel; and as we learn from Exo 4:23, emphatically in antithesis to Pharaoh's own firstborn.
In the inn - Or "resting place." See Gen 42:27 note.
Met him, and sought to kill him - Moses was attacked by a sudden and dangerous illness, which he knew was inflicted by God. The word "sought to kill" implies that the sickness, whatever might be its nature, was one which threatened death had it not been averted by a timely act. Zipporah believed that the illness of Moses was due to his having neglected the duty of an Israelite, and to his not having circumcised his own son; the delay was probably owing to her own not unnatural repugnance to a rite, which though practiced by the Egyptians, was not adopted generally in the East, even by the descendants of Abraham and Keturah. Moses appears to have been utterly prostrate and unable to perform the rite himself.
Sharp stone - Not "knife," as in the margin. Zipporah used a piece of flint, in accordance with the usage of the patriarchs. The Egyptians never used bronze or steel in the preparation of mummies because stone was regarded as a purer and more sacred material than metal.
Cast it at his feet - Showing at once her abhorrence of the rite, and her feeling that by it she had saved her husband's life.
A bloody husband - Literally, "a husband of blood," or "bloods." The meaning is: The marriage bond between us is now sealed by blood. By performing the rite, Zipporah had recovered her husband; his life was purchased for her by the blood of her child.
So he let him go - i. e. God withdrew His visitation from Moses.
Moses sent Zipporah and her children back to Jethro before he went to Egypt, Exo 18:2. The journey would have been delayed had he waited for the healing of the child.
All the elders - The Israelites retained their own national organization; their affairs were administered by their own elders, who called a public assembly Exo 4:31 to hear the message brought by Moses and Aaron.