A Commentary, Critical, Practical, and Explanatory on the Old and New Testaments, by Robert Jamieson, A.R. Fausset and David Brown  at sacred-texts.com
exo 13:2THE FIRST-BORN SANCTIFIED. (Exo 13:1-2)
Sanctify unto me all the first-born--To "sanctify" means to "consecrate," to "set apart" from a common to a sacred use. The foundation of this duty rested on the fact that the Israelites, having had their first-born preserved by a distinguishing act of grace from the general destruction that overtook the families of the Egyptians, were bound in token of gratitude to consider them as the Lord's peculiar property (compare Heb 12:23).
exo 13:3MEMORIAL OF THE PASSOVER. (Exo 13:3-10)
Moses said unto the people, Remember this day--The day that gave them a national existence and introduced them into the privileges of independence and freedom, deserved to live in the memories of the Hebrews and their posterity; and, considering the signal interposition of God displayed in it, to be held not only in perpetual, but devout remembrance.
house of bondage--literally, "house of slaves"--that is, a servile and degrading condition.
for by strength of hand the Lord brought you out from this place--The emancipation of Israel would never have been obtained except it had been wrung from the Egyptian tyrant by the appalling judgments of God, as had been at the outset of his mission announced to Moses (Exo 3:19).
There shall no leavened bread, &c.--The words are elliptical, and the meaning of the clause may be paraphrased thus:--"For by strength of hand the Lord brought you out from this place, in such haste that there could or should be no leavened bread eaten."
exo 13:4month Abib--literally, "a green ear," and hence the month Abib is the month of green ears, corresponding to the middle of our March. It was the best season for undertaking a journey to the desert region of Sinai, especially with flocks and herds; for then the winter torrents had subsided, and the wadies were covered with an early and luxuriant verdure.
exo 13:5when the Lord shall bring thee--The passover is here instituted as a permanent festival of the Israelites. It was, however, only a prospective observance; we read of only one celebration of the passover during the protracted sojourn in the wilderness [Num 9:5]; but on their settlement in the promised land, the season was hallowed as a sacred anniversary [Jos 5:10], in conformity with the directions here given.
exo 13:8thou shalt show thy son in that day, saying--The establishment of this and the other sacred festivals presented the best opportunities of instructing the young in a knowledge of His gracious doings to their ancestors in Egypt.
exo 13:9it shall be for a sign unto thee upon thine hand, &c.--There is no reason to believe that the Oriental tattooing--the custom of staining the hands with the powder of Hennah, as Eastern females now do--is here referred to. Nor is it probable that either this practice or the phylacteries of the Pharisees--parchment scrolls, which were worn on their wrists and foreheads--had so early an existence. The words are to be considered only as a figurative mode of expression.
that the Lord's law may be in thy mouth, &c.--that is, that it may be the subject of frequent conversation and familiar knowledge among the people.
exo 13:12FIRSTLINGS OF BEASTS. (Exo 13:11-16)
every firstling, &c.--the injunction respecting the consecration of the first-born, as here repeated, with some additional circumstances. The firstlings of clean beasts, such as lambs, kids, and calves, if males, were to be devoted to God and employed in sacrifice. Those unclean beasts, as the ass's colt, being unfit for sacrifice, were to be redeemed (Num 18:15).
exo 13:17JOURNEY FROM EGYPT. (Exo 13:17-21)
God led them not through the way of the land of the Philistines, although that was near, &c.--The shortest and most direct route from Egypt to Palestine was the usual caravan road that leads by Belbeis, El-Arish, to Ascalon and Gaza. The Philistines, who then possessed the latter, would have been sure to dispute their passage, for between them and the Israelites there was a hereditary feud (Ch1 7:21-22); and so early a commencement of hostilities would have discouraged or dismayed the unwarlike band which Moses led. Their faith was to be exercised and strengthened, and from the commencement of their travels we observe the same careful proportion of burdens and trials to their character and state, as the gracious Lord shows to His people still in that spiritual journey of which the former was typical.
exo 13:18God led the people about, through the way of the wilderness of the Red Sea, &c.--This wondrous expanse of water is a gulf of the Indian ocean. It was called in Hebrew "the weedy sea," from the forest of marine plants with which it abounds. But the name of the Red Sea is not so easily traced. Some think it was given from its contiguity to the countries of Edom ("red"); others derive it from its coral rocks; while a third class ascribe the origin of the name to an extremely red appearance of the water in some parts, caused by a numberless multitude of very small mollusca. This sea, at its northern extremity, separates into two smaller inlets--the eastern called anciently the Elanitic gulf, now the gulf of Akaba; and the western the Heroopolite gulf, now the gulf of Suez, which, there can be no doubt, extended much more to the north anciently than it does now. It was toward the latter the Israelites marched.
went up harnessed--that is, girded, equipped for a long journey. (See Psa 105:37). The Margin renders it "five in a rank," meaning obviously five large divisions, under five presiding officers, according to the usages of all caravans; and a spectacle of such a mighty and motley multitude must have presented an imposing appearance, and its orderly progress could have been effected only by the superintending influence of God.
exo 13:19Moses took the bones of Joseph with him--in fulfilment of the oath he exacted from his brethren (Gen 50:25-26). The remains of the other patriarchs (not noticed from their obscurity) were also carried out of Egypt (Act 7:15-16); and there would be no difficulty as to the means of conveyance--a few camels bearing these precious relics would give a true picture of Oriental customs, such as is still to be seen in the immense pilgrimages to Mecca.
exo 13:20encamped in Etham--This place is supposed by the most intelligent travellers to be the modern Ajrud, where is a watering-place, and which is the third stage of the pilgrim-caravans to Mecca. "It is remarkable that either of the different routes eastward from Heliopolis, or southward from Heroopolis, equally admit of Ajrud being Etham. It is twelve miles northwest from Suez, and is literally on the edge of the desert" [Pictorial Bible].
exo 13:21the Lord went before them--by a visible token of His presence, the Shekinah, in a majestic cloud (Psa 78:14; Neh 9:12; Co1 10:1), called "the angel of God" (Exo 14:19; Exo 23:20-23; Psa 99:6-7; Isa 63:8-9).