I have not said that a Guru is not necessary. But a Guru need not always be in human form. First a person thinks that he is inferior and that there is a superior, all-knowing, all powerful God who controls his own and the world’s destiny and worships him or does bhakti. When he reaches a certain stage and becomes fit for enlightenment, the same God whom he was worshipping comes as Guru and leads him onward. That Guru comes only to tell him, ‘That God is within yourself. Dive within and realize’. God, Guru and the Self are the same.Realization is the result of the Master’s (Guru’s) grace, more than teachings, lectures, meditations, etc. They are only secondary aids, whereas the former is the primary and essential cause. Guru’s grace is always there. You imagine it to be something somewhere high up in the sky, far away and which has to descend. It is really inside you in your Heart, and the moment, by any of the methods, you effect subsidence or merger of the mind into its source, the grace rushes forth, spouting as from a spring from within you. Contact with jnanis is good. They will work through silence. A Guru is not the physical form. Hence His contact remains even after the physical form of the Guru vanishes. After your bhakti to God has matured you, God comes in the shape of a Guru and from outside pushes your mind inside, while being inside as Self, He draws you there from within. Such a Guru is needed generally, though not for very rare and advanced souls.One can go to another Guru after one’s Guru passes away. But after all, Gurus are one, as none of them are the form. Mental contact is always the best. Satsang means association with Sat or Reality. One who knows or has realized Sat is also regarded as Sat. Such association is absolutely necessary for all. Sankara has said,“In all the three worlds there is no boat like satsang to carry one safely across the ocean of births and deaths.”Guru not being physical, His contact will continue after His form vanishes. If one Jnani exists in the world, His influence will be felt by or benefit all people in the world, and not simply His immediate disciples. As described in Vedanta Chudamani, all the people in the world can be put under four categories: The Guru’s disciples, bhaktas, those who are indifferent to Him and those who are hostile to Him. All these will be benefited by the existence of the Jnani —each in his own way and to various degrees.
From the book, Divine Grace Through Total Self-Surrender by D.C. Desai, Ramana Maharshi read out the following quotations by Paul Brunton :
Divine Grace is a manifestation of the cosmic free will in operation. It can alter the course of events in a mysterious manner through its own unknown laws, which are superior to all natural laws, and can modify the latter by interaction. It is the most powerful force in the universe. It descends and acts only when it is invoked by total self-surrender. It acts from within, because God resides in the Heart of all beings. Its whisper can be heard only in a mind purified by self-surrender and prayer. Rationalists laugh at it, and atheists scorn it, but it exists. It is a descent of God into the soul’s zone of awareness.
It is a visitation of force unexpected and unpredictable. It is a voice spoken out of cosmic silence - It is ‘Cosmic Will which can perform authentic miracles under its own laws’. In truth, God and the Guru are not different. Just as the prey which has fallen into the jaws of a tiger has no escape, so those who have come within the ambit of the Guru’s gracious look will be saved by the Guru and will not get lost; yet, each one should by his own effort pursue the path shown by God or Guru and gain release.
Each seeker after God should be allowed to go his own way, the way for which he alone may be built (meant). It will not do to convert him to another path by violence. The Guru will go with the disciple in his own path and then gradually turn him onto the Supreme path at the ripe moment. Suppose a car is going at top speed. To stop it at once or to turn it at once would be attended with disastrous consequences.