”It is very well known that by the powers of his austerities and the blessings of the Supreme Lord, the sage Svetasvatara was able to know the Supreme Lord and systematically revealed his realization to those humble sages who were in groups living in his Ashram.”
tapaih prabhavad deva-prasadac ca
brahma ha svetasvataro ‘tha vidvan
atyasramibhyah paramam pavitram
provaca samyag rsi-sangha justam
PURPORT BY SRI KRSNA BALARAM SWAMIJI
Performance of austerities purifies one from sins and when one becomes purified the Lord blesses one to realize Him in truth. When the Lord is realized all knowledge of Him manifests automatically. Bookish knowledge cannot lead one to realization of the Absolute Truth. One has to depend on the mercy of the Lord, which comes in the form of an authentic Spiritual Master. When a scripturaly authentic Spiritual Master is accepted, then the Lord recognizes the services. One must concentrate and serve the Lord in such a way that He recognizes the services. This verse proves that a Spiritual Master has to be either directly authorized by the Supreme Lord or through the indirect process of the ancient scriptures. No one should whimsically occupy the post of a Guru by the popular votes of an unqualified congregation. The Lord should either directly authorize or His stated codes in the scriptures should authorize a true Spiritual Master then He will be able to impart transcendental knowledge to the candidate. Besides this there is no other way to receive spiritual initiation.
[Svetasvatara Upanisad, 6.21, KBS0100]