If the sentence is one of command, either forbidding a crime or vice, or enjoining an act of prudence or benevolence, it is not figurative. If, however, it seems to enjoin a crime or vice, or to forbid an act of prudence or benevolence, it is figurative. “Except ye eat the flesh of the Son of man,” says Christ, “and drink His blood, you have no life in you.” This seems to enjoin a crime or a vice; it is therefore a figure, enjoining that we should have a share in the sufferings of our Lord, and that we should retain a sweet and profitable memory of the fact that His flesh was wounded and crucified for us.
On Christian Doctrine, Book 3, Chapter 16, Paragraph 24
newadvent.org/fathers/12023.htm
Seems to me Augustine here is merely giving his definition of what he believes “figurative” and “literal” is, and gives his opinion of what verse 53 “seems” to say. This is a very selective quote of Augustine’s that does not harmonize with other statements he made concerning the real presence.
So lets look at this again… the Jews were having a hard enough time understanding how Jesus “came down from heaven,” let alone that he was “the bread that came down from heaven”. Jesus could have stopped right there with these statements and the Jews would never have believed him. Then Jesus continued and said that he was “the living bread that came down from heaven”, as opposed to the manna in the desert. But he didn’t stop there, he said “the bread I will give is my flesh for the life of the world”. Then he says unless you “eat the flesh of the Son of Man and drink his blood, you do not have life within you”.
Can you explain why Jesus felt that it was necessary go so much further with the “bread come down from heaven” idea, why he didn’t just leave it at that to make his point, if as you say, the point was symbolic, meaning we should just believe in him in spirit to gain life. Why did Jesus continue develop this idea by comparing eating the living bread to “eating his flesh and blood” and not only that, but linking the eating with real food, “my flesh is true food and my blood is true drink”.
Many disciples said “this saying is hard, who can accept it?” They clearly understood what he was implying, that is why many left him. Jesus asks “does this shock you?”.
Then Jesus asks, “what if you were to see the Son of Man ascending to where he was before?”, connecting this to “the bread that came down from heaven”. Nobody saw Jesus come into the world as He was born of a woman, “is this not Jesus the Son of Joseph, do we not know his father and mother?” If they could see him ascending to where he was before, would they finally believe? Or would they continue in unbelief?