यदक्षरं वेदविदो वदन्ति विशन्ति यद्यतयो वीतरागाः। यदिच्छन्तो ब्रह्मचर्यं चरन्ति तत्ते पदं संग्रहेण प्रवक्ष्ये ॥

yad akṣharaṁ veda-vido vadanti viśhanti yad yatayo vīta-rāgāḥ yad ichchhanto brahmacharyaṁ charanti tat te padaṁ saṅgraheṇa pravakṣhye

That which is declared indestructible by the Veda-knowers, that which the controlled and passion-free enter, that desiring which Brahmacharya is performed, that path I will declare to thee with brevity.

In plain words: Krishna says he will briefly describe the path to the eternal reality. Scholars of the Vedas (the ancient holy texts) call it indestructible. Self-controlled people who are free of craving reach it, and people live a disciplined, celibate student life (Brahmacharya) because they want it.