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 16:1MURMURS FOR WANT OF BREAD. (Exo. 16:1-36)
they took their journey from Elim--where they had remained several days.
came unto the wilderness of Sin--It appears from Num. 32:1-42, that several stations are omitted in this historical notice of the journey. This passage represents the Israelites as advanced into the great plain, which, beginning near El-Murkah, extends with a greater or less breadth to almost the extremity of the peninsula. In its broadest part northward of Tur it is called El-Kaa, which is probably the desert of Sin [ROBINSON].
exo 16:2the whole congregation . . . murmured against Moses and Aaron--Modern travellers through the desert of Sinai are accustomed to take as much as is sufficient for the sustenance of men and beasts during forty days. The Israelites having been rather more than a month on their journey, their store of corn or other provisions was altogether or nearly exhausted; and there being no prospect of procuring any means of subsistence in the desert, except some wild olives and wild honey (Deu 32:13), loud complaints were made against the leaders.
exo 16:3Would to God we had died by the hand of the Lord in the land of Egypt--How unreasonable and absurd the charge against Moses and Aaron! how ungrateful and impious against God! After all their experience of the divine wisdom, goodness, and power, we pause and wonder over the sacred narrative of their hardness and unbelief. But the expression of feeling is contagious in so vast a multitude, and there is a feeling of solitude and despondency in the desert which numbers cannot dispel; and besides, we must remember that they were men engrossed with the present--that the Comforter was not then given--and that they were destitute of all visible means of sustenance and cut off from every visible comfort, with only the promises of an unseen God to look to as the ground of their hope. And though we may lament they should tempt God in the wilderness and freely admit their sin in so doing, we can be at no loss for a reason why those who had all their lives been accustomed to walk by sight should, in circumstances of unparalleled difficulty and perplexity, find it hard to walk by faith. Do not even we find it difficult to walk by faith through the wilderness of this world, though in the light of a clearer revelation, and under a nobler leader than Moses? [FISK]. (See Co1 10:11-12).
exo 16:4Then said the Lord unto Moses--Though the outbreak was immediately against the human leaders, it was indirectly against God: yet mark His patience, and how graciously He promised to redress the grievance.
I will rain bread from heaven--Israel, a type of the Church which is from above, and being under the conduct, government, and laws of heaven, received their food from heaven also (Psa 78:24).
that I may prove them, whether they will walk in my law, or no--The grand object of their being led into the wilderness was that they might receive a religious training directly under the eye of God; and the first lesson taught them was a constant dependence on God for their daily nourishment.
exo 16:13at even the quails came up, and covered the camp--This bird is of the gallinaceous kind [that is, relating to the order of heavy-bodied, largely terrestrial birds], resembling the red partridge, but not larger than the turtledove. They are found in certain seasons in the places through which the Israelites passed, being migratory birds, and they were probably brought to the camp by "a wind from the Lord" as on another occasion (Num 11:31).
and in the morning . . . a small round thing . . . manna--There is a gum of the same name distilled in this desert region from the tamarisk, which is much prized by the natives, and preserved carefully by those who gather it. It is collected early in the morning, melts under the heat of the sun, and is congealed by the cold of night. In taste it is as sweet as honey, and has been supposed by distinguished travellers, from its whitish color, time, and place of its appearance, to be the manna on which the Israelites were fed: so that, according to the views of some, it was a production indigenous to the desert; according to others, there was a miracle, which consisted, however, only in the preternatural arrangements regarding its supply. But more recent and accurate examination has proved this gum of the tarfa-tree to be wanting in all the principal characteristics of the Scripture manna. It exudes only in small quantities, and not every year; it does not admit of being baked (Num 11:8) or boiled (Exo 16:23). Though it may be exhaled by the heat and afterwards fall with the dew, it is a medicine, not food--it is well known to the natives of the desert, while the Israelites were strangers to theirs; and in taste as well as in the appearance of double quantity on Friday, none on Sabbath, and in not breeding worms, it is essentially different from the manna furnished to the Israelites.
exo 16:32Fill an omer of it to be kept for your generations--The mere fact of such a multitude being fed for forty years in the wilderness, where no food of any kind is to be obtained, will show the utter impossibility of their subsisting on a natural production of the kind and quantity as this tarfa-gum [see on Exo 16:13]; and, as if for the purpose of removing all such groundless speculations, Aaron was commanded to put a sample of it in a pot--a golden pot (Heb 9:4) --to be laid before the Testimony, to be kept for future generations, that they might see the bread on which the Lord fed their fathers in the wilderness. But we have the bread of which that was merely typical (Co1 10:3; Joh 6:32).