What is it?

Now look at this verse ----- Exodus 16.14-15: "When the layer of dew lifted, there on the surface of the wilderness was a fine flaky substance, as fine as frost on the ground. When the Israelites saw it, they said to one another, 'What is it?' For they did not know what it was. Moses said to them, 'It is the bread that the Lord has given you to eat.'"

So what is it? I understand it is bread from heaven ---- but what does that mean? It is almost as if a bunch of flaky crackers are laying on the ground. So you go around and pick up some wheat thins to get you by for the day ---- amazing! But there is this important distinction, it says that it is bread from heaven [Ex 16.4] and not bread from the earth [or Egypt, the store, Wal-Mart]. So if it is from heaven and not from the earth, what is God trying to say to us? Does it go back to Genesis 3.17-19?