Isn't It a Metaphor?

When people wrongly take jesus literally, he corrects them and explains what he means. And conversely, when people rightly take him seriously, he confirms and repeats. An example will be in john chapter six, where christ is talking about the need to have faith in him. He hasn't begun to say they need to eat his flesh, right? So that's why i'm not convinced. The original eye witnesses believed he meant what he said. This is the only example in scripture where christ's disciples abandon him over a doctrinal teaching. That's just something interesting, i think.