Bhagavad Gita · Sankhya YogaChapter 2, Shloka 38 (2.38)

Three pairs — one equanimity. Pleasure and pain (experience), gain and loss (outcome), victory and defeat (success and failure). Treating all three alike. Shankaracharya: rāga-dveṣau api akṛtvā — without attachment or aversion (liking or opposing).

"Naivaṃ pāpam avāpsyasi" — you will not incur sin. This is a direct answer to Arjuna's greatest fear (1.36 — "only sin will come to us"). Krishna says: sin comes not because of the action, but because of the spirit of the action. Duty done with equanimity does not bind one with sin.

Ramanuja's explanation: Knowing the eternal self as distinct from the body, keeping an unchanging mind amid the inevitable pleasure and pain, gain and loss, victory and defeat of war, begin the battle without desire for fruits such as heaven, purely from a sense of duty. Doing so, you will not incur sin — that is, samsara, which is suffering — you will be freed from the bondage of samsara.

Shankaracharya's explanation: This teaching is prāsaṅgika (incidental to the context); the arguments from svadharma were worldly reasoning; the main subject of the section is the vision of the highest truth, which is concluded in the next shloka.