The united one, abandoning the fruit of action, attains stable peace; the non-united, acting by desire, attached to the fruit, is bound.

Contrast between yogī and non-yogī. Yuktaḥ — united — tyaktvā karma-phalam — abandoning fruit of action — obtains śāntim naiṣṭhikīm — stable, definitive peace.

Ayuktaḥ — non-united — acts kāma-kāreṇa — by desire as motive — phale saktaḥ — attached to fruit — is nibadhyate — bound. The difference is not in acting or not, but in attachment or non-attachment. Same action, different interior produces different consequences.