Idea: The one-man town. Just came to me.

It is definitely an interesting idea!

Here are a few thoughts off the top of my head that could factor in:

Pride - The man feels that he can live up to the standards of the King of Life by himself, without community.

That might fit the idea of the true "loner faithful" that I think you kind of implied.

However, a few other ideas could include maybe the guy feels that he has the calling of a Steward (Pride?) and has been evangelizing a bit and maybe is trying to convert a few of his neighbors. Assuming he has made compromises for the sake of maintaining their lifestyle or convenience, all it takes is a couple of these neighbors before you are talking false priesthood.

Being in a wholly "eastern" type town makes using simple solutions like violence tricky. Could make for an interesting way to have the Dogs find a different solution for a situation that would normally be an obvious candidate for a shootout...

Or, if you want to keep it as a small pocket of Faithful and not include too many townsfolk, all it takes is one or two relatives of the man in question to set up the usual "What do they want the Dogs to do?" list... Perhaps a sibling of the stubborn fellow trying to get him to go back to the community... Or perhaps he has a wilfull child who insists on living here (for access to a particular school? the "Arts?" or something like that?) Or maybe he has a sick wife or child being cared for in a Hospital and he has more faith in Eastern Medicine than the King of Life? (That might make for an interesting similar story with a man among the Mountain People as well perhaps).

I keep trying to throw in another person, because I keep thinking (and I could be wrong) that it is pretty much a key feature that there has to be a conflict, or at least seeds of a conflict, in the works prior to the Dogs arrival, and that would seem to require at least two people to represent two sides...

Although an idea does strike me from your original notion of seeking out the man due to the need to deliver a letter... Perhaps the man was exiled, either willingly or unwillingly, and the letter is an attempt to recall him to the community? Either because they believe he suffered enough, or forgiven him, or decided they were wrong? That would set up the possibility of Pride in how the man reacts to this news?

Of course, you also need to account for the fact you players might just kidnap the man straight off and wind up in various gun battles with faithless sinners, so I guess you need to know your players' styles pretty well before springing something that is both subtle and precariously balanced. A potentially interesting drama could become a murder and flight from the TA after a single conflict :-p