The Guru is the religious teacher and spiritual guide to whose direction orthodox Hindus of all divisions of worshippers submit themselves. There is in reality but one Guru. The ordinary human Guru is but the manifestation on the phenomenal plane of the Adi-natha Maha-kala, the Supreme Guru abiding in Kailasa. He it is who enters into and speaks with the voice of the earthly Guru at the time of giving mantra. Guru is the root (mala) of diksha (imitation). Diksha is the root of mantra. Mantra is the root of Devata; and Devata is the root of siddhi. The Munda-mala Tantra says that mantra is born of Guru and Devata of mantra, so that the Guru occupies the position of a grandfather to the Ishta-devata.

It is the Guru who initiates and helps, and the relationship between him and the disciple (shishya) continues until the attainment of monistic siddhi. Manu says: "Of him who gives natural birth and of him who gives knowledge of the Veda the giver of sacred knowledge is the more venerable father. Since second or divine birth insures life to the twice-born in this world and the next." The Shastra is, indeed, full of the greatness of Guru. The Guru is not to be thought of as a mere man. There is no difference between Guru, mantra, and Deva. Guru is father, mother, and Brahman. Guru, it is said, can save from the wrath of Shiva, but none can save from the wrath of the Guru. Attached to this greatness there is, however, responsibility; for the sins of the disciple recoil upon him.

Three lines of Guru are worshipped: heavenly (divyangga) siddha (siddhangga), and human (manavangga). The kala-guru are four in number, viz.: the Guru, Parama-guru, Parapara-guru, Parameshti-guru; each of these being the guru of the preceding one. According to the Tantra, woman with the necessary qualifications may be a guru, and give initiation. Good qualities are required in the disciple, and according to the Sara-sangraha a guru should examine and test the intending disciple for a year. The qualifications of a good disciple are stated to be good birth, purity of soul (shuddhatma), and capacity for enjoyment, combined with desire for liberation (purushartha-parayanah). Those who are lewd (kamuka), adulterous (para-daratura), constantly addicted to sin (sada papa-kriya), ignorant, slothful, and devoid of religion, should be rejected.

The perfect sadhaka who is entitled to the knowledge of all Shastra is he who is pure-minded, whose senses are controlled (jitendriyah), who is ever engaged in doing good to all beings, free from false notions of dualism, attached to the speaking of, taking shelter with, and living in the supreme unity of the Brahman. So long as Shakti is not fully communicated (see next note) to the shishya's body from that of the guru, so long the conventional relation of guru and shishya exists. A man is shishya only so long as he is sadhaka. When, however, siddhi is attained, both Guru and Shishya are above this dualism. With the attainment of pure monism, naturally this relation, as all others, disappears.