Krishna continues to appeal to Arjuna's warrior nature. He says that this specific war is a massive, once-in-a-lifetime opportunity. It came 'yadṛcchayā' (by its own accord/unsought). The Pandavas didn't start the war; it was forced upon them by Duryodhana's tyranny. For a warrior, fighting a righteous, defensive war is seen as an open door to heaven (svarga-dvāram apāvṛtam). Therefore, Kshatriyas who get such an opportunity should consider themselves lucky (sukhinaḥ).