Battlemaster is very similar to Crusader Kings, so instead of calling a religious value "faith points", it might work better to call it "piety", instead. This wording change makes it congruous with the honour and prestige system already in effect. Like honour and prestige, it could unlock various actions at various levels.
What those actions should be, are offensive abilities, that can be used to disadvantage hostile foreign realms, thus promoting the use of priests as tools of intrigue. The writing of scrolls is my favourite idea, for such an ability.
