Since John’s Gospel has no eucharistic institution story—only a washing of feet account—like the Synoptic Gospels do, the author of this Gospel presents a long sermon by Jesus on the bread of life. This discourse is filled with eucharistic overtones and Old Testament imagery.
The original “bread that came down from heaven” was the manna, which God gave his people in the desert. For the Johannine author to write that Jesus is the “bread that came down from heaven” is to claim that Jesus is food for God’s people to eat, like the manna they ate in the desert. However, anyone who eats this new “manna” come down from heaven will never die.
The murmuring of the crowds echoes the grumbling of the Israelites in the desert. Once they had escaped Egyptian slavery, the Israelites began to grumble against Moses and Aaron and wished that they had stayed in Egypt where there was food rather than die in the desert. Moses and Aaron tell the people that they are not grumbling against them but against the Lord. After hearing their grumbling, the Lord gives manna to his people so that they can have their fill of bread (cf Ex 16:1-15).
Just as the Israelites come to know that it is God who feeds them in the desert, so those who listen to Jesus come to understand that he is God and he feeds people with “living bread,” his flesh, which gives life to the world.
Some of those who listen to him, and those who read the Gospel with faith, recognize the eucharistic overtones and Old Testament imagery. Others see that Jesus is the “son of Joseph.” They ask, “Do we not know his father and mother?” (v 42).
For John, it all depends on faith. Faith is the window through which a person views Jesus. If one believes, then one sees the new manna that has come down from heaven “so that one may eat it and not die” (v 50). If one does not believe, then all one sees is “the son of Joseph.”