Even after Jesus miraculously fed 20,000 people with five loaves and two fish, the crowd still sought a sign from Him.  They were so focused on the temporary fulfillment found in this life they could not see that God was standing right in front of them.  Jesus reveals to them He is the bread of life, the true manna from heaven, Whom they must believe in to have everlasting spiritual fulfillment.  Simply trust in Him and they could have eternal life.  How many in the world today are so focused upon the temporal needs of now that they cannot see the answer to their emptiness is spiritual and not material?