I'm trying to remember the name of a short story. Humankind had explored the galaxy but there was one religion that was pretty much in charge. A religious inspector from that religion went to this one planet where a strange religion was taking hold. Its gospel was filled with beautiful but fantastic stories including dragons, etc. Turns out the believers know the stories aren't true but they don't care because they are beautiful stories.
"The Way of Cross and Dragon" is set in the same fictional "Thousand Worlds" universe as several of Martin's other works, including Dying of the Light, Sandkings, Nightflyers, A Song for Lya, "With Morning Comes Mistfall" and the stories collected in Tuf Voyaging. It involves a far-future priest of the One True Interstellar Catholic Church of Earth and the Thousand Worlds (with similarities to the Roman Catholic hierarchy) investigating a sect that reveres Judas Iscariot.