क्षिप्रं भवति धर्मात्मा शश्वच्छान्तिं निगच्छति। कौन्तेय प्रतिजानीहि न मे भक्तः प्रणश्यति ॥

kṣhipraṁ bhavati dharmātmā śhaśhvach-chhāntiṁ nigachchhati kaunteya pratijānīhi na me bhaktaḥ praṇaśhyati

Speedily he becometh dutiful and goeth to eternal peace; O Kaunteya, know thou for certain that My devotee perisheth never.

In plain words: Krishna says such a person quickly becomes good and finds lasting peace. He promises Arjuna ("Kaunteya," son of Kunti) that someone devoted to him is never lost.