The Bhagavad Gita

अन्तवन्त इमे देहा नित्यस्योक्ताः शरीरिणः | अनाशिनोऽप्रमेयस्य तस्माद्युध्यस्व भारत ||२-१८||

These bodies of the embodied Self, Which is eternal, indestructible and immeasurable, are said to have an end. Therefore fight, O Arjuna.

In this verse, Lord Krishna is speaking to Arjuna on the battlefield of Kurukshetra, reassuring him that while physical bodies are temporary and eventually perish, the true self (the soul) inside them is eternal and indestructible. Since death only affects the outer shell and not the essence within one's being, there is no need for grief or fear regarding mortality. Krishna uses this truth as a logical foundation to urge Arjuna to rise up and fulfill his duty by fighting against injustice.