He must be the man who has opened my inner eyes.
In his presence it is like the sun.
In his presence the inner darkness must go.
If it does not go he is not my Guru, he is a teacher.
I learn from him.
In the Bhagavad Gita this becomes very clear and beautiful.
In the first chapter, the person who later became a disciple, Arjuna, literally and actually teaches Krishna.
He says, "I know what is right, what is wrong, and I am telling you that this is not right. What you are asking me to do is not right. I want to stop this whole game."
Then early in the second chapter Arjuna says:
sisyas teham sadhi mam tvam prapannam.(II. 7)
"I am your disciple, please instruct me." Not: "You are my Guru." The expression ‘Guru’ comes later, when in the eleventh chapter Krishna reveals the cosmic form to him.
Then he says: "Jagat Guru, Hey Bhagavan. You are not only my Guru, you are the Guru of the whole universe."
Sri Swami Venkatesananda
To be continued ....