"Purity of Sustenance"
I am the living bread that came down from heaven." If you believe God can become man, shouldn't you believe God can become bread? But more than just a matter of doctrine, the real presence of Christ in the Eucharist is a means of grace to bestow life and aid us in our goal of becoming like Him. And that's the whole point; elements are transformed into the body and blood of Jesus so that recipients can be transformed into the image and likeness of God. And have His life. In short: God assumes flesh, we consume that flesh, we have life.