In the Vedic era, a Brahmin was a person who had acquired Self- knowledge or Brahma Gnana Atma Gnana.+

A Brahmin by birth,  Yogi,  Sanyasi,  Swami,  Sadhu,  monk a wandering ascetic, is not a Gnani. These are all categories belonging to the religious landscape of different ideologies.  

The one who has realized the Brahman (God in truth) is Brahmin, not the one who is born in the Brahmin caste.

In the Vedic era, a Brahmin was a person who had acquired Self- knowledge or Brahma Gnana Atma Gnana.

This was an extremely difficult path of the discipline of body, mind, and intellect, and people irrespective of their birth or class, who were dedicated to such an austere life, were recognized as Brahmins.

A great example of this tradition (that a person becoming a Brahmin, rather than born as one) is the case of Vishwamitra, a warrior (Kshatriya), who became a Brahmin after attaining Atma Jnana or Brahma Gnana or Self-Knowledge.

A smritis or code of conduct composed by Sage Atri defines Brahminhood very clearly.

"By birth, every man is a Shudra (an ignorant person). Through various types of disciplines (samskaras), he becomes a dwija (twice-born). Through the studies of scriptures, he becomes a vipra (or a scholar). Through the realization of supreme spirit (Brahma jnana), he becomes a Brahmin.”

The belief that people born in Brahmin caste, automatically become Brahmins, is a much later concept in very ancient India. Thus, Brahmin means not a caste but one who has attained Atma Jnana or Brahma Gnana.

Manduka Upanishads: -  It is very difficult to find out who is a Gnani because he bears no external mark. Neither nudity nor the yellow robe has anything to do with him.  

A Gnani cannot have the idea of renouncing the world or giving up something of the practical world because that would connote the idea of duality. Duality is merely an illusion from the ultimate standpoint. Knowing no second thing at all there remains nothing to be given up. 

If a seeker after truth receives the words of wisdom from some source, that seeker must pay the source due respect and gratitude to get the grace of the Soul, the Self. 

One does not become a Gnani by one’s matted hair. Nor does one become a Gnani by one’s clan. Even one’s birth in priest caste will not make a Gnani. One has to realize the Truth by acquiring Self-knowledge or Braham Gnana or Atma Gnana. 

The matted hair and religious robes belong to the religion. Religion is based on the false self (ego) within the false experience (waking). 

The one who has realized the Self is not the ‘I’ but the ‘Self’ is the Soul knows the religious robes and matted coiled hair is nothing to do with the Soul, the Self. 

The seeker who has realized the Soul alone is real and the world in which he exists is an illusion is worthy of the Advaitic Gnana. 

Self-knowledge or Brahma Gnana or Atma Gnana frees the Soul, the Self from experiencing the illusory of experiencing the illusory birth, life, death, and the world as a reality. 

Self-knowledge or Brahma Gnana or Atma Gnana makes the Soul, the Self unburdened and puts down the illusory load of the form, time, and space. 

Through Self-knowledge or Brahma Gnana or Atma Gnana the Soul, the Self gets disengaged from the bonds of the illusory form, time, and space in which was imprisoned. 

A Gnanis's attention is fixed on the Soul and he sees the illusion as the consciousness, the one without the second. : ~ Santthosh Kumaar