Faith in the teachings of Guru has immeasurable power to transform our barren hearts into fertile grounds of devotion. The world can be won with great intellectual capabilities; however, the grace of Guru is received only by practicing devotion with humility. Even if one were illiterate and cannot comprehend the divine teachings of the Guru, but reposes faith in him, one will benefit immensely.

Totakāchārya, one of the four disciples of Ādi Śaṅkarāchārya, attained divine knowledge through the grace of his Guru alone. Totakāchārya was a boy named Giri when Ādi Śaṅkarāchārya came into his life and accepted him as his disciple. Giri was not as bright as the other disciples - Sureshwara, Padmapāda, Hastamālaka - were, but he was devoted to his Guru and served his Guru with utmost love and dedication. Although he could not comprehend his Guru's teachings as the other disciples could, he would listen with rapt attention and in great faith. The other disciples had the misconception that Giri was less intellectual than they were, that he failed to grasp the subtle significances of the Vedic verses, and therefore they discounted him. 

One day, while Giri had gone to the river to wash the Guru's clothes, Ādi Śaṅkarāchārya waited for Giri to return before he could start his exposition. Watching this, one of the disciples questioned impatiently, "Guru ji, why should we wait for one who he is no better than a wall?" To prove Giri's faith and devotion, and to quell the pride of his other disciples, Ādi Śaṅkarāchārya in an instant illuminated Giri and called out to him.

Enlightened by his Guru's grace, Giri returned from the river in a blissful state. Right at the moment, he composed extemporaneous Toṭakāṣṭakam in praise of his Guru Ādiśaṅkarāchārya. From then on, the humble Giri went on to become Totakāchārya, one of the foremost disciples of Ādi Śaṅkarāchārya.

गु शब्दस्त्वन्धकारस्यात् रू शब्दस्तन्निरोधक: ।

(Advaya Tārakopanishad 16)

"The syllable 'gu' means darkness, and 'ru' means to destroy." Hence, one who dispels our nescience and brings to us the light of true wisdom is the Guru. A true Guru has two qualifications - Śhrortirya and Brahm Niṣhth. Śhrortirya means one who possess theoretical knowledge of the scriptures. Brahm Niṣhth means one who has realized that knowledge and is seated in the Truth. Of the two, the second criterion is the most important one, that is the Guru must be God-realized. And our scriptures have extolled the position of such true Guru to God. Shree Krishna himself reveals:

आचार्यं मां विजानीयान् नावमन्येत कर्हिचित् |

न मर्त्यबुद्ध्यासूयेत सर्वदेवमयो गुरुः ||

āchāryaṁ māṁ vijānīyān nava manyeta karhicit |

na martya buddhyā sooyeta sarva deva mayo guruḥ ||

(Shreemad Bhagavatam -11.17.27)

"Know the Guru to be Myself. Never think unfavorably about Him. Do not use your material mind to comprehend the Guru's divine actions, for all forms of God dwell within Him." When we surrender our intellect to such a true Guru, and perform actions in accordance with his teaching, we progress rapidly towards our spiritual goal, and it transforms our lives for eternity. Thus, "the true Guru is someone who has no personal desires of his own.  He has merged his will with the will of God.  Also, he is free from any pride and self-seeking.  Such a Guru does nothing of his own accord.  God becomes his guide and inspires his actions from within.  Thus, the Guru becomes an instrument through whom God does his divine work of elevating souls in the world."  Essence of Hinduism, Authored by H. H. Swami Mukundananda ji.