2.11 The Lord said  You are grieving for those who do not deserve to be grieved for. You also speak words of wisdom about the nature of the body and the self as follows:  'The ancestors fall degraded, deprived of the ritual oblations of food and water' (I. 42). There is no reason for such grief for those who possess the knowledge of the nature of the body and the self. Those who know the exact truth will not grieve for those bodies from which life has departed and for those from whome the principle of life has not departed. They do not grieve for bodies or souls.

Hence, in you this contradiction is visible - your grief at the thought 'I shall slay them?'  and at the same time your talk about righteousness and unrighteousness, as if it were the result of knowledge of the self as distinct from the body. Therefore you do not know the nature of the body nor of the self which is distinct from the body and is eternal. Nor do you know of duties like war etc., which (as duty) constitute the means for the attainment of the self, nor of the fact that this war (which forms a duty in the present context), if fought without any selfish desire for results, is a means for the attainment of the knowledge of the true nature of the self.

The implied meaning is this:  This self, verily, is not dependent on the body for Its existence, nor is It subjected to destruction on the death of the body, as there is no birth or death for It. Therefore there is no cause for grief. But the body is insentient by nature, is subject to change, and its birth and death are natural; thus it (body) too is not to be grieved for.

First listen about the nature of the self.