एवं ज्ञात्वा कृतं कर्म पूर्वैरपि मुमुक्षुभिः। कुरु कर्मैव तस्मात्त्वं पूर्वैः पूर्वतरं कृतम् ॥

evaṁ jñātvā kṛitaṁ karma pūrvair api mumukṣhubhiḥ kuru karmaiva tasmāttvaṁ pūrvaiḥ pūrvataraṁ kṛitam

Having thus known, our forefathers, ever seeking liberation, performed action; therefore do thou also perform action, as did our forefathers in the olden time.

In plain words: Krishna says the wise people of long ago knew this and kept working while seeking spiritual freedom. So Arjuna should also do his work, as they did.