Chapter II · Śloka 19
य एनं वेत्ति हन्तारं यश्चैनं मन्यते हतम् |
उभौ तौ न विजानीतो नायं हन्ति न हन्यते ||
उभौ तौ न विजानीतो नायं हन्ति न हन्यते ||
ya enaṃ vetti hantāraṃ yaś cainaṃ manyate hatam |
ubhau tau na vijānīto nāyaṃ hanti na hanyate ||
ubhau tau na vijānīto nāyaṃ hanti na hanyate ||
One who thinks this slays, and one who thinks this is slain — both of them fail to perceive the truth. This does not slay, nor is it slain.
The deepest level of the argument: not only does the body perish naturally, but the very categories of 'killer' and 'killed' do not apply to the ātman at all. Mistaking the instrument (body) for the agent (self) is the root confusion.