This is a verse from Srimad-Bhagavatam (11.17.27) spoken by Lord Krishna when He was questioned by Uddhava regarding the four social and spiritual orders of society. The Lord was specifically instructing how a brahmacari should behave under the care of a spiritual master. A spiritual master is not an enjoyer of facilities offered by his disciples. He is like a parent. Without the attentive service of his parents, a child cannot grow to manhood; similarly, without the care of the spiritual master one cannot rise to the plane of transcendental service.
The spiritual master is also called acarya, or a transcendental professor of spiritual science. The Manu-samhita (2.140) explains the duties of an acarya, describing that a bona fide spiritual master accepts charge of disciples, teaches them the Vedic knowledge with all its intricacies, and gives them their second birth. The ceremony performed to initiate a disciple into the study of spiritual science is called upaniti, or the function that brings one nearer to the spiritual master. One who cannot be brought nearer to a spiritual master cannot have a sacred thread, and thus he is indicated to be a sudra. The sacred thread on the body of a brahmana, kshatriya or vaisya is a symbol of initiation by the spiritual master; it is worth nothing if worn merely to boast of high parentage. The duty of the spiritual master is to initiate a disciple with the sacred thread ceremony, and after this samskara, or purificatory process, the spiritual master actually begins to teach the disciple about the Vedas. A person born a sudra is not barred from such spiritual initiation, provided he is approved by the spiritual master, who is duly authorized to award a disciple the right to be a brahmana if he finds him perfectly qualified. In the Vayu Purana an acarya is defined as one who knows the import of all Vedic literature, explains the purpose of the Vedas, abides by their rules and regulations, and teaches his disciples to act in the same way.
Only out of His immense compassion does the Personality of Godhead reveal Himself as the spiritual master. Therefore in the dealings of an acarya there are no activities but those of transcendental loving service to the Lord. He is the Supreme Personality of Servitor Godhead. It is worthwhile to take shelter of such a steady devotee, who is called asraya-vigraha, or the manifestation or form of the Lord of whom one must take shelter.
If one poses himself as an acarya but does not have an attitude of servitorship to the Lord, he must be considered an offender, and this offensive attitude disqualifies him from being an acarya. The bona fide spiritual master always engages in unalloyed devotional service to the Supreme Personality of Godhead. By this test he is known to be a direct manifestation of the Lord and a genuine representative of Sri Nityananda Prabhu. Such a spiritual master is known as acaryadeva. Influenced by an envious temperament and dissatisfied because of an attitude of sense gratification, mundaners criticize a real acarya. In fact, however, a bona fide acarya is nondifferent from the Personality of Godhead, and therefore to envy such an acarya is to envy the Personality of Godhead Himself. This will produce an effect subversive of transcendental realization.
As mentioned previously, a disciple should always respect the spiritual master as a manifestation of Sri Krishna, but at the same time one should always remember that a spiritual master is never authorized to imitate the transcendental pastimes of the Lord. False spiritual masters pose themselves as identical with Sri Krishna in every respect to exploit the sentiments of their disciples, but such impersonalists can only mislead their disciples, for their ultimate aim is to become one with the Lord. This is against the principles of the devotional cult.
The real Vedic philosophy is acintya-bhedabheda-tattva, which establishes everything to be simultaneously one with and different from the Personality of Godhead. Srila Raghunatha dasa Gosvami confirms that this is the real position of a bona fide spiritual master and says that one should always think of the spiritual master in terms of his intimate relationship with Mukunda (Sri Krishna). Srila Jiva Gosvami, in his Bhakti-sandarbha (213), has clearly explained that a pure devotee's observation of the spiritual master and Lord Siva as being one with the Personality of Godhead exists in terms of their being very dear to the Lord, not identical with Him in all respects. Following in the footsteps of Srila Raghunatha dasa Gosvami and Srila Jiva Gosvami, later acaryas like Srila Visvanatha Cakravarti Thakura have confirmed the same truths. In his prayers to the spiritual master, Srila Visvanatha Cakravarti Thakura confirms that all the revealed scriptures accept the spiritual master to be identical with the Personality of Godhead because he is a very dear and confidential servant of the Lord. Gaudiya Vaishnavas therefore worship Srila Gurudeva (the spiritual master) in the light of his being the servitor of the Personality of Godhead. In all the ancient literatures of devotional service and in the more recent songs of Srila Narottama dasa Thakura, Srila Bhaktivinoda Thakura and other unalloyed Vaishnavas, the spiritual master is always considered either one of the confidential associates of Srimati Radharani or a manifested representation of Srila Nityananda Prabhu.