Jesus said, “Whoever eats my flesh and drinks my blood…”
He didn’t mention at all that it’s only the substance and not the physical characteristics.
Yes, you’re right: He didn’t mention anything about it… And that’s why, in John 6, so many people left Him. You see, the ‘Bread of Life’ discourse – in its context, as it was taking place – wasn’t so much a theological seminar as it was a request, by Jesus, for folks to believe in Him. After all, the crowd had seen Him feed 5000 with 5 loaves & 2 fish; the apostles had seen Him walk on water. And now, Jesus is asking them to apply those lessons. Yes, it was a very difficult lesson to work on, but He was asking them to believe Him and trust in Him.
Who took what Jesus said and decided he meant it’s not his actual blood and flesh, with its characteristics?
And when did they decide this?
Jesus did, Himself! He ‘decided’ it at the Last Supper:
“While they were eating, he took bread, said the blessing, broke it, and gave it to them, and said, ‘Take it; this is my body.’ Then he took a cup, gave thanks, and gave it to them, and they all drank from it. He said to them, ‘This is my blood of the covenant, which will be shed for many.’” (Mark 14:22-24)
And how can one eat the “substance” of something without that substance’s “physical characteristics” included?
It’s an argument based in philosophy that, first, defines what ‘substance’ and ‘characteristics’ (well, actually, the term is ‘accidents’) are (and how the two are typically linked in a certain thing)…
How can these two things be separate?
…Ever hear someone call the Eucharist a ‘miracle’? These two things can
only be what we say they are because Jesus Himself made it so: He promised it, and He did it, and He told
us to do it in memory of Him. They can be separate only because it’s a miracle each time it happens.
Your description sounds like what other Christians do when they take the bread and wine as symbolizing his flesh and blood, not actually* being* it.
Now you’ve taken the discussion a step farther. (It’s ok: there are Catholics who, when they hear what the Church teaches, think the same thing, and then get ticked off at the person who explained it to them, as if he’s saying something untrue.)
What ‘other Christians do’ is say “this isn’t really Christ – it just symbolizes Him.” What I’m saying is that it
is really Christ. Not in terms of physical appearances (after all, it still tastes like bread, and it can still get you drunk like wine) – the appearances of bread and wine remain. But, if anything happens (and, as Catholics, we say that something
amazing does happen!), then it’s not on the order of appearances: it’s on the order of ‘substance’. The bread and wine really
do become the Body and Blood of Christ… just not under the usual appearances that we’re used to seeing with bodies and with blood.