The Function of "Weeping and Gnashing of Teeth" in Matthew's Gospel

Why did Matthew, on six different occurrences, record Jesus pronouncing judgment by employing the term "weeping and gnashing of teeth"? Interestingly, each of these occurrences is spread throughout the entire gospel. Perhaps this theological idiom was a theme that Matthew recognised as central to Jesus and his theology, taking meticulous care to include it in his gospel within the context of each occurance. In this book, I have attempted to answer not only what is the meaning of this unique phrase, but also, what theological function does this apocalyptic judgment phrase serve in the theology of Matthew.