I find it interesting alone that the assumption that someone who believes in the Bible is naturally going to lie with out swearing.
But i would expect that anyone who talks to invisible people on a regular basis may need a reminder to be honest in the real world

Affirmation is as binding in court as swearing is in court. In both cases. it's the judge who can hold a witness in contempt or even find a witness has committed perjury. What concerns me are those atheists who swear on the Bible anyway because they haven't come out as atheists yet or are too intimidated by the system to be completely honest before affirming to tell the truth.