Ch 18, Sh 50 continued-2, Bhagawad Gita, Shankar Bhashya

Only the eradication of the superimposition of name, form, etc., which are not the Self, is what has to be undertaken, but not the knowledge of the Self that is Consciousness. For it is the Self which is experienced as possessed of the forms of all the various objects that are superimposed (on It) through ignorance. It is evidently because of this that the Buddhists who uphold the view of (momentary) consciousness have concluded that there is no substance at all apart from (momentary) consciousness, and that it is not in need of any other valid proof since they hold that it is self-cognized. Therefore, what is to be undertaken is only the elimination of the superimposition on Brahman through ignorance, but no effort is needed for knowing Brahman (Consciousness), for It is self-evident! It is because the intellect is distracted by particular appearances of name and form imagined through ignorance that Brahman, even though self-evident, easily realizable, nearer than all else and identical with oneself, appears to be concealed, difficult to realize, very far and different,
But to those whose intellect has become free from external appearances and who have obtained the grace of a teacher and serenity of mind, there is nothing more blissful, manifest, well known, easily realized and nearer to oneself than this Self. And thus it has been declared, 'directly realizable, righteous,' etc. (9.2).
However, some wiseacres assert that the intellect cannot comprehend the entity called the Self since It is formless; hence, complete steadfastness in Knowledge is impossible. This is truly so for those who have not associated with a traditional line of teachers; who have not heard the Upanisads; whose intellects are too much engrossed with external objects; and who have not applied themselves diligently to the perfect means of knowledge. For those, on the other hand, who are the opposite of these, it is absolutely impossible to have the idea of reality with regard to empirical objects, which are within the realm of duality involving the knower and the known, because in their case there is no perception of any other thing apart from the Consciousness that is the Self. We have already said how this is certainly so and not otherwise. It has been stated by the Lord also, 'That during which creatures keep awake, it is night to the seeing sage' (2.69). Therefore, the cessation of the perception of differences in the form of external things is alone the cause of resting in the reality of the Self. For, that which is called the Self is never an object which is not well known, attainable, rejectable or acceptable to anyone at any time. Were that Self to be indeed not self-evident, all activities would become meaningless. For it cannot be imagined that they could be undertaken for unconscious objects like the body etc. Besides, it cannot be that pleasure is for pleasure's sake, or that sorrow is for sorrow's sake. Moreover, all empirical dealings are meant for culminating in the realization of the Self. Therefore, just as for knowing one's own body there is no need of any other (external) means of knowledge so also there is no need of any other means of knowledge, for the realization of the Self which is innermost (in relation to the body etc.). Hence it is established that steadfastness in the knowledge of the Self is a fact very well known to the discriminating people.