"One can understand the Vedic mantras only by the grace of the Lord and the spiritual master (yasya deve parā bhaktir yathā deve tathā gurau [ŚU 6.23]). If one takes shelter of a bona fide spiritual master, it is to be understood that he has obtained the grace of the Lord. The Lord appears as the spiritual master for the devotee. Thus the spiritual master, the Vedic injunctions and the Lord Himself from within—all guide the devotee in full strength. In this way there is no chance for a devotee to fall again into the mire of material illusion. The devotee, thus protected all around, is sure to reach the ultimate destination of perfection."
(Śrī Īśopaniṣad, Mantra 18, Purport)
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