Guru is an important concept in sAdhanA. While a sAdhaka's initial concept of Guru might be a person who is a teacher or a guide, this concept gets refined as sAdhanA progresses. There are certain specific qualifications for being a Guru, and these are clearly laid out in the Upanishads. The MuNDaka Upanishad describes a Guru as shrotriyam brahmaniSTham: one who is learned in the Vedas and eternally established in Brahman. There are very few teachers who meet these criteria, and I hold three such teachers as qualified to be called Gurus. They are
BhagavatpAda Sri Adi ShankarAcArya
Sri Ramakrishna
BhagavAn Sri RamaNa Maharishi
I am not aware of any Gurus who are alive today, although that does not necessarily mean they do not exist. SadhakAs frequently lack the discrimination to distinguish true Gurus from guides. Since a Guru is permanently established in Brahman, such a person will not be engaged in any activity. An Ashram may spring up around such a person, but they will be truly desireless. It is hard for most people to even imagine such a person, so with the lack of discrimination sAdhakAs accept anyone as Guru. This can lead to disappointments and difficulties in spiritual growth. While someone who has had a even a glimpse of the Eternal Truth through samAdhi can provide some guidance, they cannot call themselves a Guru. Unfortunately many teachers have sprung up calling themselves Gurus (or at least not denying the title when their students bestow it on them), and they do not keep up with their own spiritual practice. Then there are scandals and sAdhakAs are disappointed and the spiritual path itself becomes negatively perceived by the general public.
What is important for sAdhakAs to realize is that it is not necessary to have a Guru in a physical body in order to benefit from Guru. As SwAmi RAma and SwAmi JnAneshwara BhArati have written very lucidly on Guru, it is really a channel for spiritual growth. It is useful in the early stages to affix a personality to this channel, but it is very important to choose this personality wisely. The three Gurus I have listed above are all excellent choices because their lives are shining examples of the pinnacle of spiritual accomplishment. Of these, Adi ShankarAcArya has written extensively on many sacred texts, so the aspirant has access to all his teachings. Sri RamaNa Maharishi has also written his spiritual insights and recommendations, although to a lesser extent. There are many wonderful anecdotes and sayings of Sri Ramakrishna that are also very inspiring. However, it is quite difficult for a beginning aspirant to learn directly from any of these Gurus. Therefore, they are not frequently chosen as Guru. However, if one has access to a Guide who can lead one on the Path to these Gurus, then such a guide is an excellent choice.
When the light of prajnA dawns on the aspirant and the Guru chakra is opened, then all of life becomes a Guru. Interactions with a child, or even a hostile person become a channel through which Guru communicates. After all, as the Yoga SUtra says, the Seen is for experience and liberation. When the sAdhakA reaches a stage where all experience becomes an opportunity to learn the lesson that leads to liberation, then one may conclude that the Guru chakra is fully opened.
GurubrahmA shlokam
AdinAtha in HYP.