A Hermeneutical Rule of Thumb

There are fantastic events and figures in the Bible.  The authors intended some of these to be historic and others figurative.  Jesus being a “door” is figurative.  The resurrection is historical.  Balaam's ass spoke.  The talking snake in the garden is symbolic.   We need a principled way to classify these elements correctly.  In some cases, the narrative tells us outright that it's symbolic.  Sometimes common-sense can decide.  Other times, it's more vague.  

Here's a rule of thumb that correctly classifies each item on the above list.  If some event or figure is fantastic, then we should take it to be historical if:   The narrative includes (a) surprise and wonder on the part of the audience or narrator and (b) the event is ascribed to a supernatural being. Balaam's ass meets both criteria, so we should take it to be historical.  The snake does not.  The snake is not described as being possessed by Satan or miraculously enabled to speak by God. Instead, the narrative goes out of its way to describe the snake as a mere beast: "now the snake was the most cunning animal that God has made," and cursed to crawl on the ground. Neither does its speaking surprise the characters or narrator, despite the fantastical nature of a snake speaking.  So we should take the snake to be non-historical.  The resurrection, on the other hand, satisfies both criteria - it's both immensely surprising and ascribed to God, so classifies as historical.  This rubric correctly classifies the items.

Why think these criteria are true, though? Well, first - miraculously fantastic things do not happen naturally. So if the narrative describes some fantastic thing happening naturally, then there's a problem if it's taken literally, a problem the author would have recognized. For the second condition, miracles are fantastic things and are unexpected. If the narrative doesn't contemplate the audience or narrator being surprised, if a fantastic thing is just passed by, then we have a clue that it’s meant figuratively. Think of the "door" statement. If upon hearing that Jesus called himself a door, the audience burst into surprise and wonderment about the Jesus/door hybrid before them, then we'd have some evidence that the narrative meant it literally. But since it's passed by as an unremarkable comment, we know it's a figurative statement. Contrast this to the "I am the bread" statement by Jesus in John 6.  The audience did react with surprise (and disgust), providing some evidence that Jesus meant the statement in a literal way.  

Notice that the trees of Genesis would also classify as figurative using these criteria. For their ability to confer knowledge and eternal life is something that they seem to possess inherently, and not because God happens to grant eternal life on the occasion of eating the fruit. Their ability even seems to work contrary to God's will, necessitating God to set up a guard to prevent mankind from eating them after the fall. So they're figurative as well. 

There are, of course, other criteria that help determine whether an author meant an event historically or not.  This rule of thumb isn’t an infallible criteria, either.  Just a suggestive guide.  Comparative literature analysis, genre analysis, and so on are additional tools that can help settle the question of whether a text is figurative or not.