It helps in part to know the specific language you're writing in, to find a font that is compatible with the orthography.

A font that's personable with a calligraphic flair is good for prayers in general. Something like the current header font, Elli from The Font Bureau, would be good for a few lines on a poster, though perhaps a bit kitschy depending on the accompanying imagery (I can't really think of any spiritual poster I've seen that isn't kitschy), and too informal for a page of text.

Pester for a Ross Mills for a beta of this:
http://www.tiro.com/Huronia/index.html