Advaita or non-dualism as propounded by Sankara has been misunderstood and misinterpreted, according to some brAhmaNas who led an austere life and spent their time in AtmajnAna, and who tried to share their knowledge with small neighbourly groups.
As a last-ditch attempt to persuade people not to deform or ravage this magnificent philosophy (though it has some weak-spots, caused, imho, mainly because Sankara had to write bhAshyas to get his ideas over to the people in general) I am giving below the core ideas which my limited intelligence has been able to absorb from the aforesaid "chamber pravachanams or discourses" by people who shunned publicity and were contented to live in peace and go away.
1. jeevAtmA is no different from the parabrahman.
2. The jeevAtmA resides in all living things as untaintedly as the Supreme Brahman. But once the jeevAtmA is associated with or covered by the physical body-mind-intellect (and the five kOSas, according to some), the jeevAtmA becomes clouded in its vision and is no longer able to express its inherent nature through all these filters (five kOSas, or intellect-body-mind trio~ Chinmayananda often used this BMI acronym in his Gita lectures).
3. If a type of cataract operation were possible to be performed on the clouded ‘vision’ of the jeevAtmA, people could get brahmajnAna on order, may be even through internet ordering! But so far, that has not been possible and it is for the individual person to make efforts towards this objective.
4. Almost all methods prescribed in the Hindu religious canvas – from poorvameemAmsA yAgAs to the latest kundalini techniques – are helpful in a person achieving the above objective of cleansing the jeevAtmA’s vision. But the wise people do not recommend “vAmAcAra” (left-handed) practices for this purposes; the Tantra-related systems like laLitA upAsana, ucchiShTagaNapati upAsana, kALi upAsana, chAtthan sEva (very popular in Kerala), etc., are not recommended by the learned people; even the “bhagavati sEva” which is quite popular among the tabras of Kerala is not recommended. The learned people say that these prohibited practices have side-effects which are more harmful than the objective of achieving AtmajnAna through such methods; these practices dangle the “aShTa siddhis” and more often than not the practitioners are lured by these and fall into deep abyss instead of climbing the stairs of AtmajnAna.
5. Externalized “bhakti” – towards an object which is ouside of the seeker after AtmajnAna is not at all helpful. Hence, the group bhajans, mantra chantings, elaborate and showy poojas, both in temples and by individuals/groups, will not be helpful. But praying, singing bhajans or worshipping god in any form with the clear central idea that god is “within one” and not external to us, is very much necessary and a must. (It is said that the Tamil word “kaDavuL” tries to remind us that we have to ‘enter inside’ (uLLE kaDa) to find God.
6. Worshipping persons as god-equivalents is wrong path, but for those who are very poor in their spiritual evolutionary state, may be they will spend a number of births doing this, just as a toddler learns to walk properly after many a fall.
7. Gurus or Acharyas should be people with proper credentials. As a rule of thumb, it is better to avoid those who are or like publicity.
8. “nididhyAsana” or deep meditation is the only correct path and practice for gaining AtmajnAna; all the rituals and nithya/naimittika karmas prescribed for the dwija castes only help the person in doing the deep meditation more effectively.
9. One must be able to face one’s own self – with all its warts and scars - without fear and analyze one’s self by steps in order to gradually reduce and eventually remove the effects of mind and intellect on the jeevAtmA. The limitations imposed by the body like lust, gluttony, craving for bodily comforts, etc., are easier to overcome completely than those created by mind & ‘buddhi’.
10. Lastly, gaining AtmajnAna does not make a person look any different and so it is difficult to ‘spot’ such a person. He/she may be one of the millions of the common people we come across but it is difficult to know, and true to the saying “kaNTavar viNTilar”, such persons will not go about saying “I have gained AtmajnAnam”.