One cannot become a guru just by memorizing the verses of scriptures, such as the Vedas, and then concocting an explanation for them.
nayam atma pravacanena labhyo
na medhaya na bahudha srutena
yam evaisa vrnute lena labhyas
tasyaisa atma vivrnute tanum svam
Katha Upanisad (1.2.23)
Eloquent discourses, outstanding intelligence or extensive and astute hearing will not enable one to attain the Supreme Personality. The Supreme Lord selects who He wants to attain Him. Those persons alone are successful and receive His darsana.
We need to deliberate on how much of this transcendental knowledge we have absorbed. Many devotees may take shelter of the same spiritual master. Among them, some have been illuminated by transcendental knowledge, while others are still covered by ignorance. It is inappropriate to blame sri guru for this. Such a difference is based on the different qualifications and endeavours of his disciples. A teacher may give the same lesson to all students, but one student tops the class with excellent marks, while another fails miserably, and yet another barely passes. The teacher has taught them equally well, but their results vary according to their ability. In the same way, one cannot become a spiritual master simply by being a disciple, unless one has the necessary qualification.
Sri Devananda Gaudiya Matha, Navadvipa
8 March 1998