B.G 2.21
vēdāvināśinaṁ nityaṁ ya ēnamajamavyayam । kathaṁ sa puruṣaḥ pārtha kaṁ ghātayati hanti kam ॥ 2-21॥
O Arjuna, how can the Jīva who knows thus the Indestructible Lord to be (the doer), ever existing, unborn and unchangeable, think of being killed or hurting another?
Gīta Bhāshya 2.21
The words 'avinashina' and 'nitya' refer to the Lord. Word 'nashtha' is commonly used to address Jīva, as it means tainted with defect. The word 'Vēda' refers to the imparted knowledge till previous verse, that the Lord is the doer of all acts and Jīva is not an independent agent.
atō ya ēvaṁ vēda sa kathaṁ kaṁ ghātayati hanti vā। avināśinaṁ naimittikanāśarahitam। nityaṁ svābhāvikanāśarahitam athavā avināśinaṁ dōṣayōgarahitam। nityaṁ sadā bhāvinam। iti sarvatra vivēkaḥ । dōṣayukta puruṣādiṣu naṣṭaśabdaprayōgāt॥ 21 ॥
How can one who understands thus (Jîva to be eternal and dependent) think of killing or causing another to kill?
"avinâshina" - means one who does not have a destruction of the form; and "nitya" - means one who does not have a destruction of original nature;
or
"avinâshina" - means one who is untouched by defects, and "nitya" - means one who exists always.
Above said is common wisdom.
As Jîva is tainted with defects, the word 'nashta' is used to address it.
