Excerpt from Khyentse Rinpoche talk:
"How does chanting Om Mani Padme Hum help us to maintain the worth of Avalokiteśvara? Because Om-ma-ni-pad-me-hum, these six syllables, actually bring the presence of God. These six syllables manifest six kinds of experience. In order to counter and manipulate these six realms, we have Om Mani Padme Hum."