A mild and humorously formal rebuke of someone who has expressed doubt or incredulity about something one said one would or could do. The phrase is used in several places in the New Testament of the Bible. The uncommon and somewhat archaic interjection "O" is often simply rendered to "oh" in modern English. A: "Oh, wow. It looks like your shortcut really did save us a bunch of time." B: "O ye of little faith." A: "Are you sure this will work?" B: "Come on, I know what I'm doing, oh ye of little faith."