Albert Barnes Commentary Exodus 16:23

"And he said unto them, This is that which Jehovah hath spoken, Tomorrow is a solemn rest, a holy sabbath unto Jehovah: bake that which ye will bake, and boil that which ye will boil; and all that remaineth over lay up for you to be kept until the morning." — Exodus 16:23 (ASV)

Tomorrow ... - Or, Tomorrow is a rest, a Sabbath holy to Yahweh: that is, tomorrow must be a day of rest, observed strictly as a Sabbath, or festal rest, holy to Jehovah.

Bake ... - These directions show that the manna thus given differed essentially from the natural product. Here and in Numbers 11:8, it is treated in a way that shows it had the property of grain and could be ground in a mortar, baked and boiled.

Ordinary manna is used as honey; it cannot be ground, and it melts when exposed to a moderate heat, forming a substance like barley sugar, called “manna tabulata.” In Persia, it is boiled with water and brought to the consistency of honey. The Arabs also boil the leaves to which it adheres, and the manna thus dissolved floats on the water as a glutinous or oily substance.

It is obvious that these accounts are inapplicable to the manna from heaven, which had the characteristics and nutritive properties of bread.