Bhagavad Gita Chapter 2 Sloka 21 (2.21)

ವೇದಾವಿನಾಶಿನಂ ನಿತ್ಯಂ ಯ ಏನಮಜಮವ್ಯಯಮ್ ।
ಕಥಂ ಸ ಪುರುಷಃ ಪಾರ್ಥ ಕಂ ಘಾತಯತಿ ಹಂತಿ ಕಮ್ ॥೨೧॥
vedāvināśinaṃ nityaṃ ya enamajamavyayam |
kathaṃ sa puruṣaḥ pārtha kaṃ ghātayati haṃti kam ||21||
Gist of the sloka:
O Partha. Soul which has neither birth nor death; nor has any destruction at any time. When that is the case, who and how can such a soul be destroyed?
Explanation:
One who understands that - soul which is unblemished, every lasting, unchanging and also its Swaroopa; how can one kill such a person[soul]? By its very nature soul cannot be destroyed and birth/deaths happen due to Lord will, how can one get killed or kill another? We should only think about the universal force which is making the things happen.
One knows by now that the soul has neither birth/death. At the same time, we see birth and deaths in our regular life. How can one understand this contradiction? Lord Krishna explains this in the succeeding verses.