If you want to understand spiritual knowledge, you have to approach a guru. One meaning of the word guru is” weighty”. Therefore the guru is one who is “heavy” with knowledge. And what is that knowledge? That is explained in the Kathopanisad: srotriyam brahmanistham [MU 1.2.12]. Srotriyam means “one who has received knowledge by hearing the Vedas, the sruti”, and Brahma-nistham indicates one who has realized Brahman, or rather Parabrahman, Bhagavan, the Supreme Personality of Godhead.That is the guru’s qualification.