When we stop saying what we want to say, and start talking about what we are going to say, it is because what follows is either surprising or important. But English is not the only language that uses meta-comments. Even ancient Greek and Hebrew use meta-comments, and they are found in very similar contexts to what you find in spoken English. There are literally hundreds of instances of meta-comments in the New Testament, but few commentators draw attention to them or to what they are doing. One of