कर्मणैव हि संसिद्धिमास्थिता जनकादयः। लोकसंग्रहमेवापि संपश्यन्कर्तुमर्हसि ॥

karmaṇaiva hi sansiddhim āsthitā janakādayaḥ loka-saṅgraham evāpi sampaśhyan kartum arhasi

Janaka and others indeed attained to perfection by action: then having an eye to the welfare of he world also, thou shouldst perform action.

In plain words: Krishna points out that King Janaka and others reached perfection through action. Arjuna should also act, keeping the good of the world in mind.