In this week's section we read about Manna. There are several laws and concepts we learn from this "special bread".
The Torah tells us that, 30 days after the Exodus from Egypt, the Jewish people ran out of matzah (with which they had left Egypt) and had no raw materials to make more bread. So, the people demanded that Moses and Aaron give them bread.
In response to the people's demand, God told Moses to inform them that in the morning they would eat "bread from heaven." Our sages say that Moses then decreed the first of the four blessings of Birkat HaMazon, the blessing after eating bread. The second was instituted by Joshua upon entering the Land of Israel, the third by Solomon upon building the Temple, and the fourth, of rabbinic origin, was instituted by Rabban Gamliel much later.
The Torah then recounts the laws regarding how this bread would be "given": it would fall each morning upon the dew and, in turn, be covered with dew. Hence the custom of placing the Shabbat challah on a tray and covering it with a cloth during the Kiddush—sanctification—of Shabbat.
On Fridays, a double portion of manna was served: one portion for Friday itself and one for Shabbat, when it is forbidden to gather and carry it from the desert to the tents. Hence the halakha (law) of reciting the Shabbat challah blessing over two challahs, not one as on other days of the week.
Now, among the concepts we learn from the Man, beyond laws and customs, is the idea of trusting that God is the one who sustains us in two aspects: 1) God sustains us in general and, 2) God sustains us with what is necessary.
The Torah recounts that people gathered manna daily, and regardless of how much they collected, upon returning to their homes they would find exactly the amount of an Omer for each member of the family. The following day, the leftover manna would spoil, and it was necessary to gather what had fallen that day.
God could have made the manna fall weekly, monthly, or annually, so that all the manna needed for a given period would be gathered only once. However, the reason it fell daily was to teach the Jewish people to trust in God and to know that He is the One who constantly sustains us. In turn, we must understand that God provides us with everything we need, like the manna, so that even if a person gathered too much or too little, upon returning to their tent they would have just enough. It is not excessive or inappropriate effort and work (for example, working on Shabbat, or deceiving others, etc.) that yields the greatest rewards. God gives each person what they need to satisfy all their needs. And if at times it seems like little, perhaps we are not focusing on our true needs...