नियतं कुरु कर्म त्वं कर्म ज्यायो ह्यकर्मणः। शरीरयात्रापि च ते न प्रसिद्ध्येदकर्मणः ॥

niyataṁ kuru karma tvaṁ karma jyāyo hyakarmaṇaḥ śharīra-yātrāpi cha te na prasiddhyed akarmaṇaḥ

Perform thou right action, for, action is superior to inaction, and, inactive, even the maintenance of thy body would not be possible.

In plain words: Krishna tells Arjuna to do his proper work. Acting is better than doing nothing, and without action you could not even keep your body alive.