Jesus was teaching them that faith was much
deeper than signs and wonders. They needed
a bread other than the manna in the wilderness.
They had to have the bread of life that was sent
from heaven.

They said, "Lord evermore give us this bread,"
yet they were still thinking materially. They
were thinking of this bread, like the woman at
the well was thinking of the water.

And Jesus said unto them, "I am the bread of life:
he that cometh to me shall never hunger; and he
that believeth on me shall never thirst."
John 6:35