What does John 6:26 mean?
Prior to this statement, Jesus' worldly popularity has been growing. His healing miracles attracted a crowd (John 6:2). His feeding of thousands (John 6:9–14) inspired an entire mob to come looking for Him in Capernaum (John 6:22–24). With this first line of dialogue, however, Jesus will bring that surge of enthusiasm to a sudden halt. This verse summarizes the entire discussion comprising the rest of chapter 6. The people are seeking free food, not spiritual truth. As soon as Jesus begins to explain that His miracles are only meant to teach, they lose interest. Christ will describe how material things fade away, but His real purpose is to give people eternal life. This message not only stalls the crowd, it makes them angry, and as a result almost all of them will turn their backs on Jesus.John uses the term signs in reference to Jesus' miracles. A sign is something which delivers a message. It points people in a certain direction. The people's reaction to Jesus' miracles, however, is completely wrong. Rather than grasping the spiritual importance, and trusting in Jesus' authority, the people are attracted to the material aspects. They are seeing the miracle, but missing the meaning. This is like running towards a colorful metal shape along the side of the road, because it is pretty, not bothering to read it, and missing the danger it is meant to warn us of. Ironically, the same people who seek Jesus due to His miraculous signs will demand even more proof once His claims interfere with their preferences (John 6:30).
Christ's actions here also send an important message to modern churches: we should not attempt to "keep" attendees with entertainment and hand-outs. Rather, we should use such things as a way to introduce people to the gospel, and then let them decide how they want to respond to Christ.