य एनं वेत्ति हन्तारं यश्चैनं मन्यते हतम्।
उभौ तौ न विजानीतो नायं हन्ति न हन्यते।।2.19।।
He who thinks of this One as the killer, and he who thinks of this One as the killed both of them do not know. This One does not kill, nor is It killed.
Bhagvan says that your thinking that Bhishma, Drona etc will be killed by you and that you will be their killer is false and wrong. How?
The topic of the discussion is dehi (the one who is embodied = shariri = atman). If someone thinks this atman as the killer, subject of the action killing, or if someone thinks it to be killed, object of the action of killing, then neither of them know this atman correctly. By the killing of body, both of them assume that’I am the killer’ or ‘I am the killed’. Neither of them know that atman which is the object of I-thought (aham-pratay-vishayam) due to non-discrimination. Why so? Because the atman is changeless, it cannot kill or get killed. Thus atman can neither be subject nor object of the action of killing due to sheer reason of being changeless.
But how is this atman changeless? [in next shloka]
It is important to understand the meaning of word atman. It is used in the sense of Brahman as well as in the sense of jiva. Brahman is everything. So Brahman cannot be embodied because body is not different from Brahman so as to have a cognition of embodied. The topic of discussion is dehi=shariri=embodied. This is also known as jiva. Thus, in the current topic of discussion, wherever atman comes, one should not confuse with Brahman. Brahman is the swa-roopa of both atman and the world. Brahman is known through shastra alone. Atman (=jiva) is self-evident. This is beautifully explained by the use of word aham-pratyaya-vishayam for atman. Elsewhere in Brahm Sutra Bhashya too, Shankaracharya refers to pratyagatma (indwelling Self) as asmat-pratya-vishayam. Thus, the following can be said as the conclusion:-
Both world and jiva are non-different from Brahman. But Brahman is different from both of them. Just as pot is not different from clay but clay is different from pot. Just as clay is the swa-roopa of pots, Brahman is the swa-roopa of world. As far as jiva is considered, the apt analogy is that of snake and rope and not of clay-pot.