Some practices involving chanting or music can put people into a trance-like hypnotic state, which can also make them very suggestible, used in psychotherapy (hypnotherapy) to delve into the subconscious mind. Religious chanting (e.g. Gregorian chanting) can also put someone into a hypnotic state.
When I used to go to church as a child the chanting of the priest during the service was very relaxing and almost mesmerizing. In mass religious gatherings (e.g. Kumbha Mela in India) and other huge festivals thousands of people can be worked into a complete religious frenzy by the chanting, dancing, hand clapping and drumming. Heady stuff.