Wow, I'm commenting somewhat-in-depth on another player's character! Not something I do often enough, I admit...but, in a way, this is a new thing in the RP, since the only other clergy-type characters I've seen here have been one of Yui's sisters and Inari, both of them eastern-style.
I'd like to note that approval of this character will be confirming that another of the current religious systems has continued into the SARP time period. Considering how long this and other systems have already been around, and that we don't know how far into the future the RP is, this is not entirely unlikely.
But, unless it will be okay to be vague about details, I would like a wiki page started on what the "People of the Book" believe, out of curiosity (it seems a mixture of traditional Christian monkhood and Jewish faith) and in case some players wish to incorporate it into their current or future characters. The Shinto religion already being used on Yamatai seems to have made it more-or-less intact and un-mixed, but I can't be sure about this one.
As for the character himself, Za'as sounds like you've done a good job of making a "Book"-ish character without copying the guy beyond his role on the ship. Questions: How has being sheltered affected his knowledge of machines, spaceflight, computers, modern culture, and things that may not have been available in a monastery? How about his interactions with other people, what are his mannerisms and how do they differ from people outside of the monastery? Lastly, how is he going to be useful on the ship? While he wasn't usually directly involved in ship affairs, Book brought his firearms training and odd connections to the Alliance in Firefly in addition to his religious beliefs. I suppose this question will be answered somewhat by my first one, though.
Editing note: On the wiki, you need to add his name to the header in what is currently "-name- In Roleplay".