I've been toying with a way of comparing theory and faith, but I'm not yet sure how well it works. Summary: Theory is to faith as our concept of physical necessitation is to that of social obligation.

We think of theory and faith as both imparting an obligation to believe. But the sense of "obligation" is different in each case. Theory borrows its sense of "obligation" from how we think about the natural world. Faith borrows its sense of "obligation" from how we think about the social world.

The sense of "obligation" in theory is that of natural necessity. We have an intuition that, in the natural world, forces act on things to necessitate changes in their states. (I'm talking about a primitive folk notion of "necessitate", here, not the determinism of Newtonian mechanics.) Analogously, we are obliged to believe a theory because the force of reason, like a natural force, pushes us to do so.

The sense of "obligation" in faith is that of duty, trust, and deference to those who deserve it. If someone deserves our trust, then it feels wrong, or insolent, or at least rude, to demand independent evidence for their claims. Certain kinds of social relations impose a duty on one party to act as though the word of the other party were beyond doubt. Faith is the duty that we owe to God to trust him, which duty we have in virtue of the fact that we are indebted to him for our existence. And this faith is rewarded, just as one would expect to be rewarded for showing due deference to one's social superiors.