Notes on the Bible, by Albert Barnes, [1834], at sacred-texts.com
Exodus Chapter 13
Sanctify unto me - The command is addressed to Moses. It was to declare the will of God that all firstborn were to be consecrated to Him, set apart from all other creatures. The command is expressly based upon the Passover. The firstborn exempt from the destruction became in a new and special sense the exclusive property of the Lord: the firstborn of man as His ministers, the firstborn of cattle as victims. In lieu of the firstborn of men the Levites were devoted to the temple services.
Abib - April. Compare Exo 12:2. It is uncertain whether this name was ancient or given then for the first time. It is found only in the Pentateuch, six times as the name of the first month, twice in the sense of young wheat, hence its etymology, namely, the month when the wheat began to ripen. The name resembles the Egyptian Epiphi, and may possibly have been derived from it.
The Canaanites - Five nations only are named in this passage, whereas six are named in Exo 3:8, and ten in the original promise to Abraham, Gen 15:19-21. The first word "Canaanite" is generic, and includes all the Hamite races of Palestine.
Hebrew writers have generally regarded this as a formal injunction to write the precepts on slips of parchment, and to fasten them on the wrists and forehead; but other commentators are generally agreed that it is to be understood metaphorically. The words appear to be put into the mouths of the parents. They were to keep all the facts of the Passover constantly in mind, and, referring to a custom prevalent ages before Moses in Egypt, to have them present as though they were inscribed on papyrus or parchment fastened on the wrists, or on the face between the eyes. If, as may be inferred from Deu 6:7-8, Moses adopted this custom, he would take care to warn the people against the Egyptian superstition of amulets. Modern Israelites generally allege this precept as a justification for the use of phylacteries.
An ass - The ass could not be offered in sacrifice, being an unclean animal: possibly the only unclean animal domesticated among the Israelites at the time of the Exodus. This principle was extended to every unclean beast; see Num 18:15.
Thou shalt redeem - The lamb, or sheep, was given to the priest for the service of the sanctuary.
Firstborn of man - The price of redemption was fixed at five shekels of the sanctuary: Num 3:47, where see the note.
Harnessed - More probably, "marshalled" or "in orderly array." There is not the least indication that the Israelites had been disarmed by the Egyptians, and as occupying a frontier district frequently assailed by the nomads of the desert they would of necessity be accustomed to the use of arms. Compare Exo 1:10.
Etham - The house or "sanctuary of Tum" (the Sun God worshipped especially by that name in Lower Egypt), was in the immediate vicinity of Heliopolis, called by the Egyptians the fortress of Zar, or Zalu (i. e. of foreigners); the frontier city where the Pharaohs of the 18th dynasty reviewed their forces when about to enter upon a campaign on Syria. The name Pithom (see Exo 1:11) has precisely the same meaning with Etham, and may possibly be identified with it.
Pillar of cloud - The Lord Himself did for the Israelites by preternatural means that which armies were obliged to do for themselves by natural agents. The Persians and Greeks used fire and smoke as signals in their marches, and in a well-known papyrus, the commander of an Egyptian expedition is called "A flame in the darkness at the head of his soldiers." By this sign then of the pillar of cloud, the Lord showed Himself as their leader and general Exo 15:3, Exo 15:6.