The Vedas earnestly exhorts the novice that in order to learn the science of self-realisation one must take shelter of a spiritual master. The knowledge of yoga, like any other science or knowledge can be transmitted in its unadulterated form, only by an experienced and genuine teacher and cannot be learnt by rote exclusively from a book. We speak of a spiritually enlightened preceptor and mentor who is in line with Sage Patanjali's teachings. Just anyone posing to be a guru without requisite qualification is rejected in the Vedas as an unauthorised preceptor. Patanjali also stresses this point saying the guru should be not only knowledgeable but of ideal character also.
Many aspects of yoga can be self taught. However the esoteric features of yoga are incomprehensible to the novice and can be revealed only by an expert. Besides, even the more obvious, even self-taught aspects can be seen from a new perspective and its in-depth import grasped through the elaborations from a guru, which otherwise would remain undiscovered. The real advantage of receiving guidance from a guru is to save precious time and great endeavour. The truth is, just as a blind cannot lead another blind person; nor can one cross the ocean catching a dog's tail; similarly a novice who is blindly moving in the realm of profound knowledge can on his own not arrive at the right conclusions and unequivocal answers. Nor can one understand the esoteric concepts with insufficient guidance.
A beginner is like someone fallen into a deep dark well, how can he ever manage to climb out of the well on his own. Our ignorance is compared to a deep dark well, the one who throws us the rope of succour is the guru. The Sanskrit word 'guru' (gu= filth, ru = shatter), means one who shatters our attachment to the accumulated filth of material existence, thus the freeing the mind to experience higher dimensions of percipience and existence . Guru also means heavy, because he carries the weight of responsibility to open the spiritual vision of conditioned souls with the torchlight of realised knowledge. When 'guru' is conjugated in the following manner, 'gur' = to raise, lift up, 'u' = interjection of compassion, sing hymns, names of Shiva and Brahman, then it means one who lifts our state of consciousness by teaching us to sing mantras (hymns). Or he himself solicits to the Supreme Brahman and Lord Shiva for the spiritual awakening of his disciples.