It's what's termed metaphorically speaking- Also: "Psalm 91:4 He will cover you with His feathers; under His wings you will take refuge" Now God is a big chicken. Again, a metaphor.
So if you're not a son of Levi you've nothing to worry about.
Metaphorically speaking.
Just refuting your implied claim that Purgatory was an invention of the Middle Ages. Rather, the idea of a refining (purging) fire goes back to the early Church.