Background
The history books of every  country often contain black pages describing certain negative values prevalent  in human society. Indian history is no exception. India gave to the world the  crest jewel of philosophy ‘Advaita Vedanta’, or Philosophy of Non-dualism which  enunciated primary unity of all existence. But this high philosophy was honored  more in its breach than in observance in the country of its origin which thus  became the home of the worst type of social evil called untouchability.

The practice of untouchabilty  created different classes of people called the outcastes and the higher castes  in Indian society. The segregated class came to be known as outcastes or  Chandalas. The other sections of the population were unapproachable by and  un-seeable to them. Such segmentation was not made on any rational ground. The  distinction among the people as higher and lower led to various forms of social  tension some of which are witnessed even today. (Also read When caste was not a  bad word  http://www.esamskriti.com/essay-chapters/When-caste-was-not-a-bad-word-1.aspx)

Given this gloomy background, a  person with the stigma of being an outcaste could hardly be expected to dare  speak the words of Vedanta and that too to a person of a higher caste who also  happened to be the expounder of non-dualistic philosophy particularly in that  period of Indian history. (Please note that the highly respected Swami Ramdev  belongs to the backward caste using British inspired modern day connotations of  Caste). But this is what exactly happened in the life of Sri Adi Sankaracharya.

Advaita Philosophy:
The essence of Sankara’s  non-dualistic philosophy is that Brahman, the Absolute, alone is real; this  world is unreal and the Jeeva or the individual soul is not different from the  Brahman. It emphasized that Brahman is One only and the whole Universe is the  expression of that only One and the apparent plurality of the world of objects  is due to ignorance.

Sankara and the Outcaste
One Summer noon at Varanasi Sri  Sankara after taking a bath in the holy Ganga was proceeding towards the temple  of Lord Viswanath along with his disciples. The Great Acharya saw an outcaste,  a Chandala, coming along with his dogs in his way. He told the Chandala “get  away, get away - move away, move away”.

These innocent looking remarks  led to an unexpected questioning from the Chandala and caused Sankara to give  out to the world an immortal poem entitled ‘Maneeshaa Panchakam’ which elaborated the Vedantic ideas and brought into focus that even a person  belonging to a low caste could rekindle the light of wisdom in the greatest  among the great teachers.

Sri Sankara’s encounter and  dialogue with the outcaste on the streets of Varanasi were of immense and  eternal significance.

Issues raised by the Outcaste
The Chandala asked Sankara:
1. By saying ‘Move away, Move away’ do you wish to move  matter from matter or you mean to separate spirit from the Spirit? You have  established that the Absolute is everywhere - in you and me and yet you want me  to get away from you as if I were different. Is it this body, built up of food  that you wish to keep at a distance from that body which is also built up of  food? Or do you wish to separate Pure Awareness which is present here from the  same Awareness present there?
2. Does it make any difference to the sun when it is  reflected in the waters of Ganga or in the dirty waters of the cesspools in the streets of Chandalas? Is there any difference in the space as such, be it in a  golden pot or in a mud pot? In the self-existing ocean of Blissful  Consciousness, in the inner self, where there are no waves of agitating  thoughts, how can there be this great delusory distinction - this is a Brahmin  and this is an untouchable?

SANKARA’S RESPONSE
These words of the Chandala  struck the Sadguru with astonishment. As a teacher of Advaita propagating the  one Infinite Self in all, he immediately recognized that the Chandala taught  him his own philosophy correctly.

HE THEN AND THERE COMPOSED THE  FIVE VERSES ENTITLED ‘MANEESHAA PANCHAKAM’ REITERATING THAT EVEN THOUGH  A CHANDALA, HE HAVING EXHIBITED CLEAR PERCEPTION OF THE BRAHMAN, IS INDEED THE  GURU OF THE JAGADGURU.

These five verses have been collectively given the name  ‘Maneeshaapanchakam’, maneesha means deep conviction and panchakam means  fivefold... The word ‘maneeshaa’, meaning ‘conviction’ appears in the last line  in all the five verses.

In these verses which expound the  wisdom of the Mahavakyas declared in the four Vedas, Sankara not only responded  to his critique but also sent a timeless and universal message that  distinctions based upon social, moral, ethical and other similar considerations  have no relevance in the Upanishadic teachings.

Synopsis of Maneeshaa Panchakam:
Sankara proclaims in his poem  that it is his firm conviction that he alone is his Guru, be he a Chandala or a  Brahmin who:
1. has realized that he is not the seen, but that he is the one consciousness that illumines all experiences during the waking, dream and deep sleep states, the one consciousness that is the sole witness of the entire play of the universe, the one consciousness which is the very life spark in all forms - from the creator down to the ant. (This verse elucidates the Mahavakya ‘Pragnaanam Brahma’ - Consciousness is Brahman).
2. in his direct experience of the Supreme, has understood that the entire Universe is merely a play of the Pure consciousness, projected by his ignorance, expressed in the three moods of his mind (sattwa, rajas, and tamas), while he himself is that Brahman. (This verse elucidates the Mahavakya ‘Aham Brahma Asmi’ - I am Brahman, the one who has awakened from his limited sense of ego and realized the Supreme).
3. reflecting upon the fact that this world of change is permanently in a state of flux, quietens his mind devoid of all disturbing thoughts and constantly contemplates upon Brahman, has burnt up all his past  and future residual vasanas in the fire of pure consciousness, has offered  his body to live through and exhaust its present destiny. (This verse       elucidates the Mahavakya - ‘Tat Tvam Asi’ - That Thou Art).
4. with his mind made completely tranquil and meditates upon that which expresses itself as ‘I’, the subjective individuality in all creatures - plant, animal, human etc. That by whose light body, mind and senses are all enlivened to activity, even though by themselves they  are inert and insentient, that which illumines everything as sun from behind a bank of clouds. (This verse elucidates the Mahavakya ‘Ayamatma Brahma’ - This self in me is the infinite reality).
5. Having thus given the gist of the entire Advaita  Vedanta based on the four Mahavakyas Sri Sankara concludes by saying that during the moments of quietitude a Yogi’s mind gains that ocean of bliss, the Brahman, the reality. He emphasizes that the one who dissolved his individual  intellect in the eternal ocean of bliss is not only a knower of Brahman but Brahman Himself. A Yogi of this status is worshipped even by the King of Gods. Such a God-man-on-the-earth is “my Guru - sole guide and light - be he an outcaste, be he a Brahmin - this is my firm conviction -Maneeshaa mama” declares Adi Sankara.

Mythological Twist
The mythological depiction of the  incident which to some extent clouds its real message says that Lord Siva  Himself with Parvati appeared before Sankara in the forms of an outcaste and  his wife to test the depth of Sri Sankara’s spiritual understanding. Late Swami  Ranganathanandaji Maharaj of Sri Ramakrishna  Mission opines that if the tradition is removed from the story it is one of the  most poignant human stories and a memorable incident in Sri Sankara’s life.

Conclusion
To summarize, the five verses of  Adi Sankara’s Maneeshaa Panchakam convey that the body is not to be confused  with the self or consciousness and that any one who exhibited the awareness of  the Reality was indeed the Guru and worthy of the highest respect irrespective  of whether he was an outcaste or a Brahmin by birth. Sri Sankara was of the  firm view that there were no distinctions in the Pure consciousness, the  Brahman. Advaita,  the non-dualistic philosophy elaborately expounded by Sankara, does not  recognize differences between people based on caste, creed, religion, gender  etc since we are all the manifestations of the same Brahman.