The Jews were the ones who had brought up the matter of the manna; Jesus now contrasts it with the true bread from heaven of which the manna was only a type. It merely sustained the body as any other food would do; the true bread from heaven would feed the spirit and the soul. Maclaren notes that the bread that perishes feeds a life that perishes. Those who ate the manna died, but those who eat of the bread of heaven will live forever.

“eat” = aorist tense indicating a once-and-for-all action. What is the significance of the tense Jesus used for this verb? When we are saved, we are saved forever. If we fall, we do not need to get saved all over again — we just get cleansed of our sins so we can be back in fellowship with a holy God.