Tibetan Buddhist Prayer Wheels are filled with the mantra of Avalokiteshvara, the Buddha of great compassion that says: Om Mani Padme Hum which directly translates to "Conscious Knowledge of the Existence of the Jewel of the Divine Spark in the Human Heart."
Om Mani Padme Hum has various interpretations, but Dalai Lama has said: "It is very good to recite the mantra Om mani padme hum, but while you are doing it, you should be thinking on its meaning, for the meaning of the six syllables is great and vast:
"Om": symbolizes the practitioner's impure body, speech, and mind; it also symbolizes the pure exalted body, speech, and mind of a Buddha.
"Mani": meaning jewel, symbolizes the factors of method: (the) altruistic intention to become enlightened, compassion, and love.
"Padme": meaning lotus, symbolize wisdom.
"Hum": indicating invisibility, symbolizing purity which must be achieved by an indivisible unity of method and wisdom.
These wheels when spun in a clockwise motion bring healing and blessings. These prayer wheels have been believed to cure diseases and clear karma. In Tibet and Nepal, Prayer Wheels have been made for many centuries in a wide range of sizes and styles - from hand-held and table-top wheels, all the way up to giant eight or twelve foot Prayer Wheels with diameters of five to six feet in Buddhist Stupas and Monasteries. They are often arranged in long rows which people will spin as they walk clockwise around the building, reciting what is considered to be one of the most profound and beneficial mantras;
There is a saying: “anyone who recites the six syllables while turning the dharma wheel at the same time is equal in fortune to the Thousand Buddhas.” It is also said that "turning the prayer wheel once is better than having done one, seven, or nine years of retreat" The prayer wheel is a very powerful merit field; one accumulates extensive merit and purifies obstacles.