It is the institution of guru-parampara, the guru-disciple lineage, that has, from generation to generation and down the centuries, closely safeguarded and handed down the living experiences of the seers of the upanishadic age. Spiritual knowledge is a matter of guru-parampara. It is handed down from the guru to the disciple. Study the Brihadaranyaka Upanishad. You will have a comprehensive understanding.
Gaudapadacharya imparted self-knowledge to his disciple Govindacharya; Govindacharya to his disciple Shankara; and Shankara to Sureswaracharya. Matsyendranath imparted divine knowledge to his disciple Gorakhnath, Gorakhnath to Nivrittinath, and Nivrittinath to Jnanadev. Totapuri imparted knowledge to Sri Ramakrishna, and Sri Ramakrishna to Swami Vivekananda. It was sage Ashtavakra who moulded the life of Raja Janaka. It was Gorakhnath who shaped the spiritual destiny of Raja Bhartrihari. It was Sri Krishna who made Arjuna and Uddhava become established on the spiritual path when their minds were in an unsettled state.
All the great ones had their teachers. Swetaketu learnt the nature of Brahman from sage Uddalaka; Maitreyi from the great seer, Yajnavalkya; Bhrigu from Varuna; Narada Rishi from Sanatkumara; Nachiketas from Yama; Indra from Prajapathi. Several others humbly went to the wise ones, observed strict Brahmacharya, practised rigorous discipline and learnt Brahmavidya from them.
All sophistry and ostentation, learning and conceit, have to be cast aside before the disciple approaches the guru. The whole personality of the pupil should be effaced if the wisdom of the teacher is to illumine the self of the pupil.
It is said in the Svetasvatara Upanishad: “To that great one who has supreme devotion to God and as much devotion to the guru as to God, do the truths become illumined.”
Now, open your eyes and note carefully what is going on in this world in all walks of life. Even a cook needs a teacher. He serves under a senior cook for some years. He obeys him implicitly. He pleases his teacher in all possible manner. He learns all the techniques of cooking. He gets knowledge through the grace of the senior cook, his teacher.
A junior lawyer wants the help and guidance of a senior advocate. Students of mathematics and medicine need the help and guidance of a professor. A student of science, music or astronomy wants the guidance of a scientist, a musician or an astronomer. When such is the case with ordinary secular knowledge, what about the inner spiritual path wherein the student has to walk alone with closed eyes.
The spiritual path is thorny, rugged and precipitous. It is enveloped in darkness. The guidance of a guru who has already trodden the path is imperatively necessary. He will be able to throw light on the path and remove obstacles.