The section of the book beginning with these verses and continuing into chapter 14 recounts the development of a spirit of discontentment among the people, and their consequent murmuring against Moses and against the Lord. This murmuring, we are meant to understand, became a continuing characteristic and had a cumulative effect. It was not merely that the people murmured once or twice. They developed a murmuring, complaining spirit, and it was this that came to a climax at Kadesh Barnea, when they failed at a critical time of opportunity. They were turned back by God into the wilderness, and kept there for forty years. Israel finally entered into the Promised Land, but that generation of Israel did not, and were not allowed to enter by God. The lesson is not that they were finally lost, but that they were disqualified in the purposes of God—a grim and solemn reality. This murmuring, complaining, critical spirit, it is clear, got into them, and did something to them, rendering them progressively incapable of rising to their divine calling until, at a moment of crisis, they crashed.

[….]

The fact that this next instance of murmuring follows immediately after the incident recorded in verses 1–3 may suggest, that “the unbelieving and discontented mass did not discern the chastising hand of God at all in the conflagration which broke out at the end of the camp, because it was not declared to be a punishment, and was not preceded by a previous announcement.” This seems quite likely; otherwise it would be necessary to interpret the murmuring in this chapter as having reached such an extreme pitch that divine judgment was swift and general; whereas the pattern un folded in this and following chapters indicates rather that it had a cumulative effect, leading to the grim pronouncement at Kadesh Barnea (14:1ff.).

The spirit of murmuring becomes specific in these verses, and its cause attributed to the rabble among the people (this seems to be the force of the phrase “mixed multitude,” which one commentator renders as “riff-raff”). This rabble-rousing element among the people certainly spread a major disaffection throughout the camp. As Calvin comments, the contagion of vice easily spreads. But the responsibility for this disaffection fell upon Israel, and as the following verses show it was Israel, not merely the “rabble,” who were punished. The weariness they expressed with what they felt to be a monotonous diet of manna, and their disparagement of it, as they longed for the Egyptian fare they had known—fish in plenty and a variety of vegetables—kindled the divine anger.

One would have thought that Israel would never have forgotten the terrible conditions of their slavery in Egypt and the horrors, privations, and tortures that had made life such a misery for them, and would have been content with any change from that, let alone the dignity of a high calling and destiny and the provision of a faithful and bounteous God. But no; they were actually looking back to these Egyptian experiences as if they had been a paradise for them (v. 5).

From this we may learn that looking back on “the good old days” is always a matter of wearing rose-colored glasses. The one word to describe the attitude of those who do so is humbug! It was, of course, the existence of the false among the true in Israel that caused the trouble, for this is always a fruitful source of infection. The truth is, the spiritual destiny is intolerable for a worldly people to contemplate—hence the telltale phrase in verse 6, “nothing at all except this manna,” even when what follows (vv. 7–9) describes that manna as a pleasant, God-given food sent with the dew of heaven, and described in Psalm 78:24ff. as “the bread of heaven” and “angels’ food.” There are those for whom “nothing except manna” is heaven itself, and every kind of joy, and others for whom it is sheer hell and unbearable; for manna is a heavenly food, and to appreciate heavenly food one needs a heavenly taste.

James Philip and Lloyd J. Ogilvie, Numbers, vol. 4, The Preacher’s Commentary Series (Nashville, TN: Thomas Nelson Inc, 1987), 124, 126–127.