That is where Jesus wants to move His hearers in Capernaum, and us this morning - beyond daily bread to true, eternal bread, to see the Bread of Life hidden behind life's daily bread. Jesus wants to bring them, and us, from barley bread to living Bread, and to do that He has to break through three barriers. The first barrier is the belly. Do not labor for the food which perishes, but for the food which endures to eternal life, which the Son of Man will give to you. There is perishable food and eternal food.
Perishable food is what refrigerators, freezers, preservatives, and expiration dates are all about.
Even the manna in the wilderness had an expiration date - exactly one day, except on the Sabbath day when it lasted two. And if the people tried to store it an extra day, it turned foul and full of worms. Perishable food feeds perishable life. That puts both food and the belly in perspective. The foods we eat do not last forever, and neither do the bodies that eat them.