Vivekachudamani 34

tam aradhya gurum bhaktya prahva prasrayasevanaih |
prasannam tamanuprapya prcchejjñatavyamatmanah ||
(Sankaracarya's Vivekachudamani 34)

Worship that guru with deep devotion and when the guru is pleased with your surrender, humility, and service, approach and ask for what you must know.

"Discipline... Disciple means discipline. The word discipline comes from disciple, or disciple comes from discipline. So unless there is discipline, there is no question of disciple. This discipline must... That should be uniform. Otherwise, sisya... sisya, the word sisya, it comes from the root, verb, sas-dhatu. sas. sas means ruling. From this word, sasana. Sasana means government. sastra. sashtra means weapon, and sastra, scripture, and sisya... These things have come from the one root sas-dhatu. So sas-dhatu means ruling under discipline. There is another English word, that "Obedience is the first law of discipline," or something.

What is the supreme perfection of human life? To attain Love of Godhead. He is known as Visaya Vigraha Bhagavan. How can you understand Him? By the mercy of Asraya Vigraha Bhagavan, or acharya or Guru, What do they do? What is their business? The guru's only business is only to guide disciples to the Supreme Personality of Godhead.

So if that guru doesn't do speak about the creator, if he doesn't speak about the Name, fame, qualities, paraphernalia, nectarean pastimes of Visaya Vigraha Bhagavan, can anybody know or understand them? If that acharya doesn't speak about Grantha avatar, Srimad Bhagavatam, can anybody understand the teachings given there, in tattva? No. The Supreme Lord is there, His Name is there, His mantra is there. They all have descended in this material world, incarnated here. Unless explains our dharma to disciple, it will never be effective.

So there is absolute necessity of accepting a bona fide guru. What is dharma of sisya? Disciple is always humble. Guru does teach - disciple hears. Sravanam Kirtanam. Unless you hear how can you practice our dharma, what bhakti you'll have? What you have heard from a guru only that you'll do. This is eternal process, Gurudevas kirtan, disciple's humble hearing. This eternal flow is known as srauta dharma, hearing dharma, and this is mercy of the Mahanta Guru.

"So, such a Mahanta Gurus are Sankaracarya, Ramanucarya, Madhavacarya, Azhwars and Nayanmars. Out of his causeless mercy he came here, and through his mercy we could understand this. So we should glorify and do Guru Puja for him instead of fashionable gurus which are sprouting like mushrooms to benefit money and gold from disciples.

A guru's duty should be:-

na dhanam na janam na sundarim 
kavitam va jagad-isha kamaye 
mama janmani janmanishvare 
bhavatad bhaktir ahaituki twayi

A guru should not have desire to accumulate wealth, nor desire beautiful women nor want any number of followers. The only duty of a guru is hanker to have causeless devotional service, birth after birth. He is very simple and not attracted by material desire or have a large number of direct disciples for his pleasure.