Augustine opens his preaching on John with an image that the Fathers had loved since Irenaeus: among the four evangelists, John is the eagle. The other three walk on the earth with Christ in His humanity; John, alone, looks straight into the sun. The first verses of the Gospel ascend at once to where the Word is with God and is God, and the rest of the Gospel is read from that height.

He warns his African congregation that what is about to be opened is not a kind of speech they have ever heard. Human reason can climb only so far. The mind that has lived among bodies finds it hard to think of the Word who has no body and was never made. Augustine asks the people to bring their hearts to the homily, not only their minds: to listen with the longing of love and not only with the appetite for knowledge.

Tractate 26, on John chapter 6, gives Augustine's mature reading of the Bread of Life discourse. He insists on two things at once. The bread Christ gives is His own flesh, truly; and the eating of that flesh is an eating in faith, by which the believer is made one with what is received.

Why, Augustine asks, did so many disciples turn away when Christ said these words? Because they thought of His flesh as something to be torn and chewed in the marketplace, while He spoke of a feeding that is also a union, a giving of Himself that abides in those who receive Him. The sacrament of the altar is the visible sign of this giving, and the sign and the reality must not be torn apart.

From this Augustine draws the rule that will run through the rest of his teaching on the Eucharist: that the bread is not less than the Body for being sign, and the Body is not less than itself for being given under bread. To eat without believing is to eat death; to believe without eating is to refuse the form Christ chose.