In the Gospel they are following Jesus because he intrigues them. They were just fed miraculously with the loaves and fishes. Now they are getting hungry and want to eat that easily again.
This seems to be why Jesus says you are looking for me not because you saw signs but because you ate the loaves and were filled. Do not work for food that perishes but for the food that endures for eternal life, which the Son of Man will give you.
Jesus is telling them they are using their energy to get some food but they will be hungry soon, and they used all this energy for only some food. Instead of using the energy for the food for eternal life.
How much do we work for eternal life? Take a given day, and honestly examine it. If you work over 50% of the day for eternal life, then you are answering Jesus plea in the gospel today to work for eternal life. If it is under then it should be changed.
Don’t be fooled. We can be working for eternal life in the midst of extremely busy days and events. We can pray during events, chores, driving etc. We can shut the tv or computers off for a while. We can do our jobs and careers with the focus on eternal life as we do our responsibilities.
Let us take Stephen’s example in the first reading, and look for, work for Jesus and Eternal Life during the midst of the every day life of this world, and not take our eyes off of it, and built an awesome Kingdom of God forever.