B.G 2.15

yaṁ hi na vyathayantyete puruṣaṁ puruṣarṣabha। samaduḥkhasukhaṁ dhīraṁ so'mṛtatvāya kalpate ॥ 2-15॥

O best among men, the person who remains undisturbed by these, who is equanimous in both pain and pleasure is 'dhīra', i.e. one who possesses steadfast intellect, composure, courage, and self-control, and is indeed fit for immortality.

Gīta Bhāshya 2.15

The being is the one who is lying in the city, called 'puri', i.e. body. Because of the absence of bodily connection, one who is not perturbed at any point in time is specially called 'purusha'. How? By bravery, one can learn to react with equanimity towards pain and pleasure.

ataḥ prayojanamāha yaṃ hi iti॥ yam ete mātrāsparśā na vyathayanti। puri śayameva santam। śarīrasambandhābhāve sarveṣāmapi vyathābhāvāt puruṣam iti viśeṣaṇam। kathaṃ na vyathayanti? samaduḥkhasukhatvāt। tatkatham? dhairyeṇa ॥ 15 ॥

Its (overcoming self-attachment) practical use is stated by 'yam hi' verse. The person referred here is the one who does not get perturbed by the contact of sensations. The being is the one who is lying in the city, called 'puri' i.e. body. Because of the absence of bodily connection, one who is not perturbed all the time is specially called 'purusha'. How can one overcome this disturbance? Having equanimity towards pain and pleasure. How? By bravery.

Gīta Tātparya 2.15

One can defeat death only by becoming 'purusha', i.e., understanding auspicious qualities of the Lord.

phalam āha। yaṁ hīti। na kevalam avyathāmātreṇāmṛtatvaṁ kintu puruṣam।

The benefit (of enduring pleasure and pain with equanimity) is described in 'yam hi' verse. One cannot defeat death just by getting rid of misery. One can defeat it by becoming 'purusha'.

"puru brahma guṇādhikyāt tajjñānātpuruṣaḥ smṛtaḥ"

"Brahman is called 'pura' because of increased auspicious qualities. One who has such knowledge of Brahman is called 'Purusha'".

iti pravṛtte।

–thus states the ancient text Pravrutti.

purusaraṇāt puruṣa ityarthaḥ ॥15॥

'Purusha' means one who goes after the knowledge of auspicious qualities of the Purusha.