Guru is one who removes ignorance – ‘gu’ stands for ignorance and ‘ru’ stands for dispeller. In this spiritual context guru is the person who removes the ignorance of the self. As per Vedanta a guru must have two qualifications; these are:
a. Srotriya – Srotriya means one who is well versed in Vedantic lore. Guru has to be well-versed or expert in Vedantic text to teach the student with all explanation. Our scriptures are the perfect tools to awaken the student from the realm of illusion to the state of truth. Self-realized master also uses languages of Vedanta to explain the various intense topics. Hence, the need for Guru to be well versed in the Vedantic lore.
Why Guru ?
On path of self-realization Guru creates trust in us. There is no other way to experiment on the path of realization; Guru is only proof of the divine knowledge otherwise divine knowledge has no any meaning; because effect of the knowledge is never physical or can be seen physically.
We can master the language of Sanskrit (The actual language of Vedas and other Indian scriptures) and mastery over text of various scriptures but without the grace and guidance of a Guru one can never understand the true meaning of scriptures.
Scriptures may not have answers arisen in your mind on journey on path of knowledge but your Guru has the answers.
As only a experienced teacher can teach a class or a student in a effective way; this same is applicable on a Guru also.
How a Guru is important is describe in “Sarva-vedanat-siddhanta-sarasangraha" of Shankaracharya in verse no. 254 –
When Lord is pleased with the continuous devotion and worship as prescribed in Vedas, he assumes the form of the Guru. He is mercy incarnate and he imparts the knowledge of reality and takes the aspirant across the ocean of samsara.