Arjuna is specifically asking for the characteristic of sthitaprajña - one who abides in the knowledge of the self to Lord Krsna. Does it mean there is difference between the knower of the self and one who abides in the self? That is no doubt that knowing take place in intellect, but to know that "I am ātmā" is not enough. One must abide in the notion that "I am this limitless ātmā" which śastra talked about. One must abide in this fact with no doubt. How to achieve that abidance? In Brhadāranyaka-upanisad, Yajñāvalkya told his wife Maitreyi, "ātmā vāre drstavyah śrotavyah mantavyah nididhyasitavyah" - "to realise paramātma one should do śravana, manana and nididhyāsana".
In śravana, knowledge takes place in the process of listening to the teaching of the self which is śastra. But it's not just mere listening, one should learn from a competent teacher who learned from a sampradāya - tradition of teaching to unfold the śastra systematically. Even though there are some people think that self knowledge can be discovered by one own self through meditation, but when one is having wrong notion about oneself since time beginning-less, how can one figure out the correct knowledge by one self? Therefore śastra and teacher serve as mirror for us to see our own true nature and remove the ignorance about the self which is the cause for samsāra.
But even after knowledge of the self took place in one's intellect and the same intellect which is used to wrong notions just couldn't accept the truth, then doubt will be there. Either doubt towards validity of śruti to be the means for moksa or doubt towards what śruti has said. It need to be solved by manana - analysis of teaching. Śruti herself guides us through certain prakriyā - method of analysis to remove doubt. And by the same analysis method we try to see in our daily life. Then this teaching can be firmly accepted without doubt.
After one has conviction of the teaching, one should do nididhyāsana - constant contemplation on the self knowledge in day to day life. Even though initial conviction is there, but we have been living with this habitual error not just from one janma - birth, therefore constant removal of the wrong notion through remembering the fact of my self is needed. In another word it is also called Vedantic meditation (refer to drgdrsyavivekah class regarding meditation on 4 & 9 June class archives).
Q: Didn't you say the self knowledge itself is the means for moksa, why there are still other means - sādhana?
A: It is true that by śravana itself, knowledge is taken place. But because of doubts and habitual error one has, he/she needs to go through other two means. If one is an uttama-adhikarī - one who highly qualified, he/she only need śravana.
Here is description of the one who abide in self knowledge.
śrībhagavānuvāca |
prajahāti yadā kāmān sārvān pārtha manogatān |
ātmanyevātmanā tuṣṭaḥ sthitaprajñastadocyate ||2.55||
Śribhagavān said:
When a person gives up all the desires, as they appear in the mind, happy in oneself with oneself alone, Pārtha (Arjuna)! that person is said to be one of ascertained knowledge.
When does desire arise? Desire arises when we give reality and ability to a particular object or situation for our fulfilment. And fulfilment is needed because lacking is there. Therefore for a sthitaprajñaḥ who abides in his/her nature of ever existence, awareness and limitless, in another word wholeness - pūrnatvam, what desires will he/she have?
There are two kinds of desire, binding and non-binding desire. It is called binding desire when we are emotionally depended upon. And non-binding desire when our body is still depended upon, but it doesn't further create emotional dependent. Any desire can appear in our mind because of the past samskāra - impression, therefore we don't need to blame ourself for having bad thought. But we do responsible if we start to entertain them.
Jñāni doesn't entertain them when they arise. He/she gives up (outgrown) binding desire, and up to certain extent try to fulfil desire which only to support physical survival like food, health, etc. Even though his/her physical dependent is still there but it doesn't affect emotionally. Since desire is born out of sense of incompleteness, therefore for one who abides in pūrnatvam, he/she outgrown all the desires. He/she is happy (nothing is lack-of) in wholeness which is not different from him/herself, without intrusion of external factor, therefore "jñāni is happy in oneself with oneself alone."