In plain words
Those alone are Gurus who drive out Ajñāna by a teaching that takes the form of practice.
Reading books may bring purity of citta, but the true nature of the subject is not grasped; the key to knowing fully the principle of the Ātma that lies within it is nothing but the experiences that dhyāna brings. Only if you win the Prema of the great souls, hear their teachings, do manana on them and practise nididhyāsana is it possible.
Īśvara Himself is the Guru of Gurus. By Īśvara's grace the blind man can see; the lame man can cross a mountain; the mute man has the chance to speak well. By His touch He destroys all the sins that are the fruit of karma, and moulds you anew, pure and spotless.
But human beings must offer their worship to Īśvara in human form itself. So long as there is the feeling of being human in us, to see even that which is beyond it is an impossible task. If a man tries to see a form that is beyond his level to grasp and beyond imagining, he fails. What is meant by the formless, the nirguṇa? If you ask, 'Please explain,' the answer is empty. Wonderful lectures can be given. Victory can be won in argument and debate; but all of it remains only a thing to laugh at. All such teachings are devoid of truth. They are attempts to display their own cleverness of intellect.
Seeing Īśvara's nature within the human is the fine royal road. How can one who is sunk in form establish the formless? Taking form itself as the base, it is possible to understand the formless step by step. People of small intellect, devoid of Bhakti and prapatti, may say that divinity does not come in human form, but that is not a true saying. 'Daivaṃ mānuṣarūpeṇa,' they say, do they not? For this very reason the Śrutis and Smṛtis praise human birth so highly.
Knowing oneself is itself the supreme goal, the aim of human life. Those deluded by the body ask, 'Is it a boy or an old man, a woman or a man?' Giving up such a body-feeling, the feeling of being Brahman must come. Saying 'Not this, not this,' you must come at last to know that you are Brahman itself. The Śrutis declare just this: 'Neti neti iti ātmā.' The jīva's form is nothing but a reflection of the Ātma. The jīva is truly an embodiment of immortality. Śaṅkarācārya taught this truth to the world, charmingly, in three phrases. 'Brahmasatyaṃ, jaganmithyā. Jīvo brahmaiva nāparā.' This itself is a most important spiritual teaching: the jīva is Brahman itself. Between the two there is a bond that cannot be broken. Humanness joined with the principle of Brahman is not base, is not petty, is not impure.
When man, not believing this truth, wavers this way and that, a Guru is utterly necessary for jīvas, and such a Guru is Vyāsa. Vyāsa means one who spread far and wide. It means one who taught the principle of the Ātma and brought it to all humanity. The one who spurred human beings on in the effort to know the Supreme Light that pervades the whole world is Vyāsa. Composing the Bhārata, the Bhāgavata and the rest, and writing the eighteen Purāṇas, he taught the path of worship that brings people happiness and Śānti.