The widely used meaning of the word acharya in Hinduism is teacher. The word acharya also means a person who expounds the meaning of mantras, teacher, preceptor, spiritual guide, holy teacher, a person who gives the sacred thread to a pupil, one who teaches the Vedas, one who propounds a particular doctrine, learned, venerable, an adviser or preceptor of a Vedic sacrifice, an epithet of Drona, a degree or title of proficiency, one who knows and teaches the rules, and one who leads by example.
According to Sanatana Dharma ‘acharya’ is not a person having merely the knowledge of the scriptures, but one who practices the teachings of the scriptures and knows all the practical ramifications of such practice from one’s own experience.
Swami Vivekananda said that while it was easy to find a teacher to learn secular subjects like physics, chemistry, or mathematics, it was quite difficult to find a spiritual teacher or acharya.
The reason he gave for this difficulty was that while it was sufficient for a teacher of secular subjects to have expertise in their subjects and it did not matter what their moral compass was or how their lifestyle was, in the case of a spiritual teacher it was paramount that the teacher practised what she or he taught.
Swamiji also said that when an acharya teaches spirituality, it is not just the wisdom contained in the scriptures that gets transferred from the teacher to the pupil, but a part of the spiritual energy of the teacher, in fact, a part of the teacher’s character, is transferred. That is why it is important that the acharya is established in the highest spiritual principle, the ultimate Reality, Brahman.
The Upanishads describe that the best acharya, spiritual teacher, or guru is one who is thoroughly well-versed in the scriptures, lives on alms, does not have any craving for the world, and is established in Brahman.
It was the tradition to completely emulate one’s acharya, because the life of the acharya was flawless and following in the footsteps of the acharya could easily lead one to spiritual fulfilment. In Sanatana Dharma, the word acharya has also been used as a title for great prophets or teachers like Acharya Shankara, Ramanujacharya,Madhvacharya, and so on.