Actually, Gorgias, I find your line of reasoning to be intelligent and on the right track.
How do we determine what is a metaphor and what is not? not to mention Similes and idioms?
On what bases do we decide? These are all issues dealing with the science of interpretation. Not everyone uses the skill of hermeneutics when they read their bibles. But a question like yours rarely comes up unless you are one who scrutinizes the way one makes an interpretation.
No… when Jesus said He was the Son of God, He wasn’t employing a metaphor. But the real questions is, on what bases does one decide? When dealing with figures of speech, there is a general rule of interpretation applied. Here it is: When the plain sense does not make sense, then you are probably in a figure of speech. When Jesus said, “I am the vine…” the plain and literal sense does not make sense, so we can probably conclude He was speaking in a figurative way. If He said, “I am the Son of God…” This should easily be taken at face value.
Secondly, there may be qualifying words in the immediate context that will also point you in the right direction to whether or not you are dealing with a figure of speech.
In general, the N.T. should be read at face-value until, or unless, there is something in the context that steers you into a figure of speech.
When Jesus said, “I am the bread of life He who comes to Me shall never hunger and he who believes in Me shall never thirst.” Jn. 6:35, we apply the rule: Does the plain sense make sense? that he who comes to Jesus will never literally hunger, or literally thirst again? Though that certainly may be possible, but most likely not His intended message. We all know Jesus was speaking in a figure of speech to help us understand spiritual hunger and thirst. Secondly, there is no example of anyone physically and literally “full” from eating. That would be insane.
Later on He said, “I am the bread which came down from heaven.” Okay… Was He literal bread? of course not. We are in a figure of speech. He did come down from heaven, but even that was in a spiritual sense. I don’t think Jesus physically descended upon and found His way into Mary’s belly.
He went on to say in verse 51, "I am the LIVING bread which came down from heaven. If anyone eats of this bread, he will live forever, and the bread that I shall give is My flesh, which I shall give for the life of the world. Jn. 6:51.
All of the sudden we are suppose to ignore the rule in interpretation here and believe that if anyone eats of this LIVING bread (literally)=Eucharist, they will live forever. And that literal bread is His flesh, literally. (Is that literally in that very moment?)