From: Cracked (edited)
Every cult leader, drill sergeant, self-help guru and politician knows that if you want to quiet all of those pesky doubting thoughts in a crowd, get them to chant a slogan.
It works because the analytical part of your brain and the repetitive task part operate separately and you can't do both at the same time.
You know you can't solve a complex logic puzzle if I force you to scream the chorus to any song over and over again while you're doing it. Try it.
Meditation works the same way with chants or mantras meant to calm the mind.
Shutting down those nagging voices in the head is helpful for stressed-out individuals.
It's also helpful to a speaker who wants to shut down an audience full of nagging internal voices suggesting that what he's is saying is nonsense.