Which comes first - belief or understanding?

The battle goes back to Ancient Greece and Aristotle and Plato: is the reality we perceive a cave, a mere illusion from which we need to find a way out? Or is this reality as real as it gets, with trustworthy sensory data? While Plato believed Socrates and saw the world as a veil of ignorance pulled over our eyes, Aristotle thought that everything we see, hear, touch, smell, and taste, is real.

This is the classic fight between science and religion that's been going on since Antiquity, each side taking turns in leading and losing. The competition has found its way everywhere, not only in the obvious places like church and the laboratory but also in popular culture - music and films and literature.

So I watched Angels & Demons (2009) last night. The movie is obviously about the clash between science and religion. There's also this one scene in which a member of the Swiss Guard tells Robert Langdon that people need to believe (in God) in order to understand (God). This is a very Platonic idea, whereas Aristotle thought people need to understand something first in order to believe in it.

On the one hand, it seems rational to refuse to believe blindly in anything you cannot first understand. For example, you must understand how the laws of physics work, before you believe they apply.

But aren't you making these analyses on the foundational belief that the world and laws of physics exist in the first place? In other words, you taking reality for granted - believing in it - before you even begin to try to understand how it works. Because how could it be the other way round? There's always something your mind cannot understand on the very bottom of everything, something you must believe unconditionally before you can analyze all the other questions about believing and understanding.

Or is there? What would happen if you could understand the very thing you're basing your understanding on?