Why do they still ask you to put your hand on the bible when being sworn in? Do they honestly think people would then only tell the truth?

When being sworn in, the clerk holds a Bible for the witness is asked to swear or affirm his or her intent to tell the truth … etc. If the witness wants to put his or her hand on the Bible, that's up to them

Why do they still ask you to put your hand on the bible when being sworn in? Do they honestly think people would then only tell the truth?
Post Opinion