In the Hindu faith, or Sanatana Dharma, human life is seen as a journey. A journey of the soul in the human body: from birth to death. The path followed by a person in this journey is dictated by circumstances into which they are born and the resultant Dharma they are expected to follow. Once one journey ends, the soul is reborn in another form and another journey ensues.
As Adi Shankaracharya’s Bhaja Govindam states:
पुनरपि जननं पुनरपि मरणं पुनरपि जननीजठरे शयनम् ।
इह संसारे बहुदुस्तारे कृपयाऽपारे पाहि मुरारे ॥
punarapi jananaṁ punarapi maraņaṁ punarapi jananījaṭhare śayanam.
iha saṁsāre bahudustāre kr̥payā’pāre pāhi murāre.
[Again birth, again death and again lying in the mother’s womb. This saṁsāra process is very hard to cross over. Save me, Murāri through Thy infinite kindness]
Man’s ultimate spiritual endeavor is to break out of this cycle of birth, death and rebirth. This is called attaining Mukti (मुक्ति). Each school of Sanatana Dharma (viz. Avaita, Visishtadvaita, Dvaita) prescribe the various paths towards attaining Mukti. My understanding of the role of a Guru is biased towards the school of Sanatana Dharma I am adhere to: the Advaita school.
In Advaita, attaining Mukti is attaining the state of self-realization: the realization of oneness between the self and the Infinite Brahman: that the Jivatma and the Paramatma are the same. As the Mahāvākya of the Mandukya Upanishad states: ‘अयमात्मा ब्रह्म’ [the self (atman) is brahman]. It is a state in which you experience the ultimate truth (the Brahman) and realize that the world is Mitya. As Adi Shankaracharya wrote: ब्रह्म सत्यं जगन्मिथ्या जीवो ब्रहैव नापरः [Brahman is real, the universe is mitya. The jiva and Brahman are not different].
The above idea of Mukti being an ‘experiential truth’ is very important to understand the true role of a Guru. A Guru is a teacher who enriches you spiritually and guides you along the path to self realization. A Guru not merely someone from whom you learn concepts and worldly knowledge. He / She is the one who provides worldly knowledge, instills discipline, puts you on the path of spiritual growth thereby preparing you to receive the higher knowledge.