Innermost Heart Mantra of Avalokitesvara - Garchen Rinpoche

The first known description of the mantra appears in the Kāraṇḍavyūhasūtra (“The Basket’s Display”, c. 4-5th centuries), which is part of certain Mahayana canons such as the Tibetan. In this sutra, Shakyamuni Buddha states, "This is the most beneficial mantra. Even I made this aspiration to all the million Buddhas and subsequently received this teaching from Buddha Amitabha."[15]
The sutra promotes the recitation of this mantra as a means to liberation. It states that whoever knows (janati) the mantra will know liberation as a fully enlightened Buddha. It also states that initiation into the mantra by a qualified preceptor (which is said to be a lay dharmabhanaka, vidyadhara or mahasiddha) is an important requirement for practicing this mantra. In the sutra, Avalokitesvara says that the mantra should not be given to one who has not seen the mandala.[16] This initiation is said to be open to all Buddhists regardless of class and gender, whether they be of the Mahayana or Hinayana, but not to tirthikas.[17]
The Kāraṇḍavyūhasūtra also sees the mantra as the pith or condensed expression of all "eighty four thousand Dharmas." Because of this it is called “the grain of rice of the Mahayana”, and reciting it is equivalent to reciting numerous sutras.[18]
Thus, according to Studholme, the significance of the mantra in the Kāraṇḍavyūha is mainly that it is the "innermost heart" of Avalokitesvara, and therefore is "a means both of entering into the presence of Avalokitesvara and of appropriating some of the bodhisattva’s power."[19] Its practice is said to lead numerous positive qualities including:[20]
The seeing (darsana) the bodhisattva's "thousand-fold" form,
Rebirth into the myriad worlds contained in the pores of the bodhisattva's body
Innumerable samadhis (meditative absorptions), including the samadhi of “rejoicing in loving kindness and compassion” (maitri-karuna-mudito).
The development of "great compassion" (maha karuna)
Accumulation of immeasurable merit
Accomplishment of the six perfections
Awakening (bodhi)
In this sutra, the sadaksari mahavidya (six syllabled great vidya) also appears as a goddess, “autumn yellow” in color, with four arms, with two arms holding a lotus and prayer beads, and the other two in anjali mudra. According to Studholme, these features are similar to the way the mantra Om nama shivaya is depicted in Shaiva texts, since "both are concise vidyas, the hrdayas [heart] of their respective isvaras, sui generis means of attaining liberation, universally available, though of rare value and somewhat secret. Both are also, it has been argued, conceived of as forms of pranava [divine sound]."[21]
The Kāraṇḍavyūhasūtra was translated into Chinese in the 11th or 12th century and it is part of the Chinese Buddhist canon.[22]