St. Nicholas Cabasilas was a great liturgical theologian and sacramental thinker of the 14th Century. He explains to us the difference between daily bread and the Bread of Life.
“Man lives because of food, but not in the same way in this sacred rite. Since natural food is not itself living it does not of itself infuse life into us…But the Bread of Life is himself living, and through him those to whom he imparts himself truly live.
While natural food is changed into him who feeds on it… here it is entirely opposite. The Bread of Life himself changes him who feeds on him and transforms and assimilates him into himself.” (Jean-Claude Larchet, Theology of the Body, p. 54).
Jesus taught: “I am the bread of life. Your fathers ate the manna in the wilderness, and they died. This is the bread which comes down from heaven, that a man may eat of it and not die. I am the living bread which came down from heaven; if any one eats of this bread, he will live for ever; and the bread which I shall give for the life of the world is my flesh.” The Jews then disputed among themselves, saying, “How can this man give us his flesh to eat?”
So Jesus said to them, “Truly, truly, I say to you, unless you eat the flesh of the Son of man and drink his blood, you have no life in you; he who eats my flesh and drinks my blood has eternal life, and I will raise him up at the last day. For my flesh is food indeed, and my blood is drink indeed. He who eats my flesh and drinks my blood abides in me, and I in him. As the living Father sent me, and I live because of the Father, so he who eats me will live because of me. This is the bread which came down from heaven, not such as the fathers ate and died; he who eats this bread will live for ever.” (John 6:48-58)