Om mani podm hum is one of the most famous mantras in Mahayana Buddhism, especially characteristic of Tibetan Buddhism, the six-syllable mantra of the compassion bodhisattva Avalokiteshvara.

The benefits of chanting the Buddha’s mantra of compassion are as endless as the boundless sky.
Even if you do not have a deep intellectual understanding of the Dharma, even if you only know Om Mani Padme Hum, but you live with an attitude free from the eight worldly concerns, your life will be filled to the brim with happiness. If you live with a pure attitude, free from attachment and clinging to this life, and simply spend time reciting Om Mani Padme Hum, this six-syllable mantra which is the essence of Dharma,
then this is the purest Dharma.