dehino-asmin yatha dehe kaumaram yauvnam jara। tatha dehantar-praptir- adhiras tatra na muhyati॥ 2.13 ॥

Just as boyhood, youth & old age are attributed to the soul & the embodied soul continuously passes through these cycles, similarly the embodied soul passes into another body at death. The wise man does not get deluded & bewildered with such a change.

maatra-sparshas-tu kaunteya shitosna-sukha-duhkha-dah:। agamapayino-anityas tams titiksasva bharata॥ 2.14 ॥

O Arjuna, the contacts between the senses & their objects, which give rise to the feelings of heat & cold, happiness and distress, etc. are transitory & fleeting in nature, therefore Arjuna, and one must learn to tolerate them without being disturbed or ignore them.

yam hi na vyathayanty ete purusham purusharsabha। sama-duhkha-sukham dhiram so ’mrtatvaya kalpate॥ 2.15 ॥

Arjuna, the wise human being to whom pain & pleasure, happiness and distress are alike, and who is not tormented by these contacts i.e. remains steady in both is certainly eligible for liberation & immortality.

na-asato vidyate bhavo nabhavo vidyate satah:। ubhayor api drsto ’ntas tv anayos tattva-darshibhih:॥ 2.16 ॥

The unreal has no existence, and the real never ceases to be; the reality of both has thus been perceived by the seers of the truth.

avinasi tu tad viddhi yena sarvam idam tatam। vinasam avyayasyasya na kascit kartum arhati॥ 2.17 ॥

Know that to be imperishable & indestructible, by which all this is pervaded; for none can bring about the destruction of this indestructible substance, the imperishable soul.

antavanta ime deha nityasyoktah saririnah:। anasino ’prameyasya tasmad yudhyasva bharata॥ 2.18 ॥

All these bodies pertaining to the indestructible, immeasurable and eternal living entity / soul are spoken of as perishable; therefore, fight, Arjuna.