Srimad-Bhagavatam: Canto 10 - Chapter 1 - Verse 33

Sanskrit:

नन्वर्थकोविदा ब्रह्मन् वर्णाश्रमवतामिह ।ये मया गुरुणा वाचा तरन्त्यञ्जो भवार्णवम् ॥ ३३ ॥

ITRANS:

nanv artha-kovidā brahmanvarṇāśrama-vatām ihaye mayā guruṇā vācātaranty añjo bhavārṇavam

Translation:

Certainly, O brāhmaṇa, of all the followers of the varṇāśrama system, those who take advantage of the words I speak in My form as the spiritual master and thus easily cross over the ocean of material existence best understand their own true welfare.

Purport:

One’s father is a natural object of reverence, as is a religious leader who initiates one into sacred ceremonies and instructs one in general wisdom. But ultimately the bona fide spiritual master, learned in the transcendental science and thus able to take one across the ocean of birth and death to the spiritual world — such a guru is most deserving of worship and respect, for he is the direct representative of the Supreme Personality of Godhead, as stated here.