The day after feeding the 5000, Jesus was in the synagogue in Capernaum, where He made the statement, "I am the bread of life." Later on in that discussion He said, "I tell you the truth, unless you eat the flesh of the Son of Man and drink his blood, you have no life in you. Whoever eats my flesh and drinks my blood has eternal life, and I will raise him up at the last day. For my flesh is real food and my blood is real drink. Whoever eats my flesh and drinks my blood remains in me, and I in him. Just as the living Father sent me and I live because of the Father, so the one who feeds on me will live because of me. This is the bread that came down from heaven. Your fathers ate manna and died, but he who feeds on this bread will live forever."
This teaching freaked out his listeners. The Jews had no tradition of cannibalism, and the Law of Moses required them to avoid eating or drinking blood. John records "From this time many of his disciples turned back and no longer followed him." But the Twelve did stick with Him. And I can imagine them, a long while later at the Last Supper, when Jesus gave them the bread and wine, saying "This is my body" and "This is my blood", looking at each other and thinking, 'Is this what He was talking about that day?' Probably the lights really came on for them after the Resurrection.
I don't think there is anything magical about the bread and juice. It isn't the going through the motions of Communion that makes the difference in us. But it is a reminder that our life comes from Him, our new way of life depends on Him. Our spirits must feed on Him.