Jamieson, Fausset and Brown on Numbers 21:5

5. our soul loatheth this light bread--that is, bread without substance or nutritious quality. The refutation of this calumny appears in the fact, that on the strength of this food they performed for forty years so many and toilsome journeys. But they had been indulging a hope of the better and more varied fare enjoyed by a settled people; and disappointment, always the more bitter as the hope of enjoyment seems near, drove them to speak against God and against Moses (1Co 10:9).