Moshe gave clear orders to Bnei Yisrael, “Every day finish eating the Mann. Do not save any for the following day. Have faith in HaShem for He will provide you every day with Mann.”
Do you remember the brothers, Dasan and Aviram? Moshe had to break up their fight back in Egypt. They were big troublemakers. Yet, nothing changed. Not even after witnessing amazing miracles and the grand exodus Out of Egypt.
“Why should we believe in Moshe?!” said Dasan. “Let’s save some of our Mann for the next day. I guarantee you, my dear brother, nothing will happen.”
“Sure thing,” replied Aviram. “Let’s save some of the Mann for tomorrow.”
But the next morning, they were in for an unpleasant surprise, “Absolutely disgusting!” they said with shock. “The leftovers spoiled completely. Look! They’re now full of horrible, slimy, creepy, filthy worms!”
But the other Bnei Yisrael did follow Moshe’s instructions.
Every morning, for the 40 years Bnei Yisrael wandered the desert, Mann rained down during the night and was waiting on the ground, ready to be gathered in the morning. And in the evening, HaShem sent very fat quail birds, called Slav, to satisfy their desire for meat.