Shepherd Derrial Book (born Henry Evans) was a passenger aboard Serenity, and a friend and spiritual teacher to its crew. Before his time aboard the ship, he led a life marked by violence and conflict, both inside and out, which remained a secret from the crew.
Shepherd Book’s character comes off as enigmatic at some times and pious at others. The scene in which he speaks this line, he is playfully righteous, not a combination you come across often. I thought it was hilarious!