The necessity of a guru, a man of God-realization, is felt by all seekers after reality. Even in material matters, the necessity of a teacher is felt; how much more it should be in the case of spirituality, for the path is very subtle. In the ocean of rebirth, lust and rage are the two big rocks through which the boat of life cannot pass unscathed. The thieves of greediness are waiting to steal the spiritual wealth of an individual. There will sharp showers of arrogance and jealousy and the hurricane of illusion which overturns the ship. Guru alone knows the proper way to escape these dangers and reach the other shore, for he has already arrived and has come, out of compassion, to take others to the other side of the Ocean of Samsara.
Spiritual initiation is a necessary factor in the path of spirituality. During such an initiation, a spiritual power is transmitted from the guru to the disciple. One who receives such transmitted power is a disciple, and one who transmits it is a guru. This power is very subtle but powerful. It clears doubt, extinguishes confusion, settles the mind, and the disciple reaches stability and equanimity. He finds safety in the benign smile of the guru, like the young of the kangaroo finds safety in the pouch of the mother. Such a one could stare at death without any fear, for he has reached immortality by the all-encompassing love and protection from the guru. The guru purifies understanding. The vrittis or deformities of the mind subside, and the mind resides in the higher realms of consciousness. Evil thoughts dare not approach the disciple who is steadfast in his devotion to the guru. He feels the presence of his guru everywhere and at all times. Sant Tukaram says, "Guru makes his disciple one like him. Even though the preparation takes a little time on the part of the disciple, it take no time for the guru to enter into the disciple to make him one like him." He says he cannot compare the guru to the philosopher's tone or the touchstone which only turns metal into gold, because the guru makes his disciple one like him--another touchstone.
Groping in the dark, one can never reach the light. Light will come from one who is flooded with it. By the grace of the guru, impossibilities become possibilities, and future possibilities become very near ones. The dull and slow evolution gets compressed, and that which has to be attained after many lives is at hand to the disciple now. He feels immense joy in the wide skies of ananda (bliss) where he can fly with wings of devotion and wisdom. He attains the power to say yes to good thoughts and no to bad ones. He can never be compelled to do any sinful deeds and is never attracted towards phantasms. Life which was boredom becomes a life of freedom, for he has attained the kingdom of God within. All this was possible due to the grace of guru, who took him slowly to the inner chamber of his heart and showed him the goal of life which is God.
Guru is a veritable treasure house containing rubies of wit and humor and emeralds of truth and divine grandeur. He is deep and sublime, but simple and approachable. He is a fire burning the bad karma of his devotees. Guru has the greatness of water to purify and quench the parched thirst of his disciples. He punishes through his silence and teaches through his action. His ways are as mysterious as the ways of God whom he has realized. His grace oozes forth through the pores of his body and shines through his lustrous eyes. "It is impossible to attain mukti or emancipation without the grace of the Guru," says Purandaradas. A man might be well-versed in all scriptures. He might have renounced the world and might have crucified his flesh, but Truth is revealed only to him who has become the slave to the great Master.
Unconditional surrender is the key toward success in life divine. Nobody can set a time limit for realization--it can be immediate or after many years. But it will certainly be given according to the intensity on the part of the disciple or according to the will of God to give him an instantaneous illumination. Due to conscious loving service, proper ground is prepared in the heart and mind of the disciple. He is purified. Seeing the right time, the guru will summon the disciple to his chambers and whisper in the cavity of his ear the great secret of OM. Even though the Word, as a word, the disciple has heard or read many a time, this invaluable and glorious truth vision will be revealed to him only during the imparting of OM by the guru at the auspicious moment. Thereafter, the disciple becomes calm and serene. The insurmountable difficulties which he had in conquering anger, enmity and other qualities are completely transformed into divine love and great compassion. He finds in every word a deeper depth and a higher height. In other words, he becomes immortal. What is the price of immortality? Therefore, he remains indebted to the spiritual Master for ever and ever. Such is the power of the grace of the spiritual preceptor.
Varieties of Gurus
There are various types of gurus. Sometimes their realization is the same, but the method of teaching is different. Sometimes their method of teaching is the same, but the method of initiation is different. Just as there are gradations in realizations, similarly, there are gradations in gurus. Some are vidya gurus, or the gurus who teach certain scriptures. Some are diksha gurus, who initiate into the meditation on Brahman or into spiritual practices. The real guru is one who makes the disciple realize God. Such a one could teach also, but his is a power separate from the mere teaching. Such a guru is considered as the highest. In the scriptures, twelve kinds of gurus are described:
Datuvaadi Guru teaches various austerities and penances, the practice of which can lead the disciple to the attainment of salvation. There is a strict spiritual discipline of physical exercises, rhythmic breathing, fasting, exhalation, inhalation and retaining of the breath, gazing at the tip of the nose or between the eyebrows, bringing the upward and downward breath together to generate a heat inside the body so that the kundalini, or the serpent power, can be awakened.
Chandana Guru releases the spiritual fragrance just by his presence. He is just like the sandal tree which wafts its fragrance to the adjoining trees. It is said that the bamboo and the plantain trees are incapable of being influenced by the sandal tree. Similarly, those that have no faith will not receive the fragrance of the chandana guru. It means he is capable of influencing people who are endowed with faith.
Vichaara Guru is full of wisdom, clarifies every subtle thing, removes the doubts of individuals, gives them food for thought, always teaches discrimination and appeals to the reason and intellect of people. The way becomes very clear to the disciple due to the clarity of understanding.
Anugraha Guru is the teacher who teaches just by his grace. His glance or touch has a power to purify the disciple. He need not have any scriptural knowledge nor intellectual capacity, yet he is able to purify the heart and mind of the disciple just by pouring his grace, for as soon as purity is attained, truth reveals itself to the practicant. Here it is the oceanic love of the guru that works the miracle of turning the heart and mind of the disciple Godward.
Parasa Guru is the guru like a touchstone. The touchstone changes metals into gold by a mere touch. Even an impure soul could be converted into a saint by the touch of the guru. This touch should not be mistaken as just a physical touch; in most cases it is the preparation on the part of the disciple to receive such an alchemic touch of the guru. The guru should concentrate and intend to transmit his spiritual vibrations through such a touch. It is a scientific fact that the eyes and the fingers are powerful channels through which the vibration of one individual passes to the other. So through the touch, the power of the guru passes on to the disciple. Of course, even without any preparation on the part of the disciple, many a time the touch of the guru gives him some healing, either of a physical or mental ailment which he may have. So also when sinful people touch the guru, it is said their sins are forgiven by the guru and due to their sins, the physical body of the guru suffers.
Kachchapa Guru is like a tortoise which is capable of giving nourishment to its young one just by a mere glance. This is a mythological description that applies to the spiritual imparting of the wisdom by the guru to the disciple. At any given moment, guru could pass on his spiritual vibrations to the disciple by his mere glance. "Kripa Kataksha" or the graceful look, has a very deep significance in mysticism. Such a look by the guru could inspire the disciple to rise to a very great height of spiritual experience. The glance has a soothing effect which could reveal a great truth to the disciple.
Chandra Guru is like the moon which shines in a special type of stone called the chandrakantha stone or moon-stone. The moon-stone alone reflects the rays of the moon, even though the moon is physically away from it. Similarly, this type of guru can be compared to the moon reflecting in the hearts of only specially qualified disciples even from a distance. This speaks about the jurisdiction of the rays of vibrations which are so wide and powerful as to reach long distances, yet be very cool, soothing and redeeming.
Darpana Guru is like a mirror. He is transparent and pure. No sooner does the disciple approach him, he sees himself reflected in the guru. Due to that purity, he makes the mind and heart of the disciple like a mirror in which the disciple finds his Self reflected.
Chaayanidhi Guru is like a mythological bird. On whosoever its shadow falls, that man becomes a king. Similarly, the shadow of a Chaayanidhi guru showers divine blessings on the disciple. Wherever his holy shadow has fallen, there shall always be divine vibrations.
Nadanidhi Guru is compared to a mythological rare stone known as the Nadanidhi stone. If the sound of any metal reaches it, it transforms the metal into gold. Similarly, if any devotee's cry is heard by the guru, the guru confers on him the highest blessings and knowledge.
Krauncha Pakshi Guru is compared to a huge, mythological crane or bird. It is said that this bird leaves its young ones and goes away to bring food. On its distant journey, if it once remembers its young ones, the young ones feel their hunger is satisfied. Similarly, the guru, wherever he is, if he even remembers his devotees, that is enough for their protection and spiritual upliftment.
Suryakanta Guru. When the rays of the sun pass through a magnifying glass, the cotton kept behind the crystal is burnt. Similarly, the darshan, or the sight of a Suryakanta guru burns the karma of a disciple.
Guru is infinite. Guru is not a person, but rather the supreme
principle manifesting through the person. The person manifesting
Guru is a temple of the Cosmic Mind. Salutations to Guru!

(Sadguru Dattatreya, p. 46.)