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.