This is nice. I wonder, though, why people wouldn't have then used some existing, familiar term referring to feudal obligation, instead of "faith". People were very conscious of the parallels between feudal relations, and relations between man and God. Yet I haven't heard faith described in those terms.

In support of this idea, remember that, while in the 1st thru 4th centuries AD, as well as today, there were/are a lot of questions about who wrote various books and whether they were inspired by God, these questions weren't often asked publicly in the middle ages. (There was inquiry into this during the Protestant Reformation.) If someone said in 1500 that you must have more faith in the Bible than in your observations, they might not have meant that there was this thing "faith" justifying belief in the Bible. Of course the Bible was inspired by God. Doubting the words of the Bible was perhaps not interpreted as doubting that the Bible was inspired by God, but as doubting that God was telling the truth. So faith wouldn't have needed to have anything to do with epistemology.