“Everything that needs to be said has already been said. But, since no one was listening, everything must be said again.”
–André Gide
In 2008, the psychologists Pascal Boyer and Pierre Liénard at Washington University in St Louis went so far as to claim that ritual creates a distinct attentional state in which we consider actions on a much more basic level than usual […] Ritual shifts attention from the overall pattern of events toward their component gestures. Instead of noting only that a bowl is being cleaned, the witness to a ritual might notice the acceleration of the hand across the bowl’s edge during each wiping gesture, or the way the cloth bunches and then opens as it is dragged forward and back across the surface. What’s more, the repetition of gestures makes it harder and harder to resist imaginatively modelling them, feeling how it might be to move your own hand in the same way. This is precisely the way that repetition in music works to make the nuanced, expressive elements of the sound increasingly available, and to make a participatory tendency – a tendency to move or sing along – more irresistible.
http://aeon.co/magazine/culture/why-we-love-repetition-in-music/