Perhaps, in their different ways, all of the above perspectives are equally right since, for each person, their own way is always the best. What seems to be commonly agreed upon by most seekers or students of life is that sometime, somewhere along the way, every person needs guidance and help to go beyond the level of understanding they are presently at. In this light some may say that a guru is anyone who wisely advises us whenever we need it.
For example, one day whilst walking along the street you stop to talk with an old lady tending her roses in the front garden. During the conversation she might say something very intuitive which, a few minutes later along your walk, causes some astounding realisation within you. Does this qualify the old lady as a guru, a bone fide spiritual teacher? What about a young child who makes an innocent yet most profound remark which changes the course of your life? Many such examples happen frequently and yet I do not consider such people are gurus. They may just be intuitive and innately wise. Their "teaching" was purely accidental.
Some may think - "But is it really accidental?" Aren't such things meant to be"? My response is yes, they are meant to be, but it was the receiver who gave the incident its relevance, extracting wisdom and learning from it, not the giver. One can extract learning from any thing, person or circumstance, but that does not make the thing, the person, or the circumstance a teacher.
The level of teaching I mean to infer upon a guru is where the person's guidance is totally conscious, where their insight is so great that they know you better that you know yourself. Socrates said - "Know Thyself". Did he not mean to understand yourself in all your facets? This statement equates with the yogic concept of striving for self knowledge, self realisation and thereby realisation of your common humanity.
Once a person has fully known themself, in the deepest sense, then they know others. In my experience, they know this because they consciously understand where others are at because they have been there themselves - not just day to day experience but evolutionary knowledge, spiritual knowledge, knowledge of consciousness, maturity of the soul. My teacher would frequently show me that he knew me better than I did myself. It was sometimes shocking! And yet beautifully inspiring.
Another level of guru's understanding is that they know what you need well before
you know it yourself. They may be secretly guiding you in that direction so that just when you need something - there it is. They may plant a seed in your mind, or help germinate one already there so that you move more effortlessly towards your destiny.
The real material of the guru's experience is non-worldly, not ephemeral. The knowledge the guru possesses has not come from a university or mundane life experiences - but from realisations within oneself about the purpose and meaning of life.
The method of a guru's teaching is by way of transmission, often non-verbal and invisible to the uninitiated. In the traditional yogic and tantric guru-disciple relationship, physical proximity is irrelevant since the transmission can be affected over any distance through the link which has been established by meditation practise. This is an experience not uncommon to twins and between mothers and their children who have established a deep spiritual resonance.
The traditional yoga guru is so like a mother in many ways, and visa versa. She brings into life, into the light of day, a being who comes from the darkness of pre-conception, and the darkness of the womb. Following that birth she is watching over you whenever you may be vulnerable to hurting yourself.
The mother guru's role is also to check up on you, to make sure you're not misbehaving, and to prod your conscience to do your best. They pick you up when you fall, pointing out that it wasn't really such a big deal after all. They remind you to keep going when the going gets tough and will pick you up and carry you on a long walk when you've really, really had enough. And beyond all that they continue to love you unconditionally, even if you don't ever thank them for their care.
What is this power, this attraction or force which allows such intimacy between two people? How then can it be more appropriate to call one's own mother a guru than to call a university professor a guru? Words and ideas, theory and intellect, instruction and debate are the professor's tools. But for the mother, the method of teaching is far more subtle and the lessons of life's truths are far more penetrating and permanent. Such teaching happens by way of an intimate infusion of knowledge through the closeness and two-way devotion inherent in that relationship.
In short, it is love which is the medium for the awakening and transference of that knowledge.