Evangelical commentators generally have felt that the manna was a substance unique from any other edible food ( Exodus 16:31). Some interpreters believe it was the sap-like secretion of the tamarisk tree or the secretion of certain insects common in the desert. [1] In the latter case the miracle would have been the timing with which God provided it and the abundance of it. Normally this sap only flows in the summer months. If this is the explanation, it was a miracle similar to the plagues, not totally unknown phenomena but divinely scheduled and reinforced. Even though there are similarities between these secretions and the manna, the differences are more numerous and point to a unique provision. [2][source]
The "testimony" was the tables of the Mosaic Law that Aaron later kept in the ark of the covenant (cf. Exodus 25:16). Moses told Aaron to preserve a pot of manna before the Lord"s presence ( Exodus 16:33-34; cf. Numbers 17:10-11). [3] These physical objects memorialized God"s faithful provision of both spiritual and physical foods (cf. Deuteronomy 8:3). [source][source][source]
The Israelites were not completely separate from other people during their years in the wilderness. As they traveled the caravan routes they would meet travelers and settlements of tribes from time to time. They evidently traded with these people (cf. Deuteronomy 2:6-7). Consequently their total diet was not just manna, milk, and a little meat, though manna was one of their staple commodities. [4][source]
God sought to impress major lessons on His people through the events recorded in this chapter. These included His ability and willingness to provide regularly for their daily needs and His desire that they experience His blessing. He gave them Sabbath rest to refresh and strengthen their spirits as well as ample, palatable food for their bodies: manna in the mornings and quail in the evenings. [source][source][source]