Lets say that I'm an engineer and for some reason, I feel myself inclined to medicine. So I pick up some books that I hear are taught in medical school and then read them cover to cover. I've no one to teach me, much less endorse if I've learnt it all right. At the end of my self-acclaimed learning, am I a qualified doctor? Is it okay for me to practice medicine treating patients? Is it also okay for me to start my own medical school and take students? Fortunately, law answers all these questions in the negative. It requires me to learn from an established medical school which is authorized by a body of qualified people in medicine. Only then will I be said to have any useful knowledge of medicine for application and teaching.
Now, why is it that people are mistaken to think that the same set of rules do not apply to Vedanta, which is even known to be esoteric? For some reason, there are people who have books by self-acclaimed masters or have learnt under them, who themselves are not disciples of anyone in the saMpradAya. Its no surprise then that the so-called knowledge that they have is not useful knowledge as far as the spiritual progress is concerned, not to say that its a downfall!
The saMpradAya requires, therefore, for a student to approach a shrotriya and brahmaniShTA guru, with reverence, to learn Vedanta after acquiring the sAdhana cAtuShTaya, that is the four-fold qualifications. Many are known to discard this set of qualifications also and thats another reason there is a misunderstanding of concepts and the knowledge doesn't shine forth. To draw a parallel with the above example of medical school, don't they too have a minimum set of qualifications before one attempts to learn medicine?!
What is meant by shrotriya is a master who has gained scriptural knowledge through a disciplic succession in saMpradAya and with that basis, not only knows the subject well, but also knows how to teach. This is a concept lost on many. The word brahmaniShTA describes being established in brahman or the absolute consciousness. Further, the saMpradAya says that its impossible for a non-brahmaniShTA to know if someone is a brahmaniShTA, which means that the stress here is on shrotriya. Bhagavatpada says that being a shrotriya guru is a must for one to gain knowledge, even if the guru is not brahmaniShTA, so thats how important the saMpradAya is.