Bhagavad Gita Chapter 18, Verse 42
शमो दमस्तपः शौचं क्षान्तिरार्जवमेव च | ज्ञानं विज्ञानमास्तिक्यं ब्राह्मणकर्म स्वभावजम् ||
śamo damas tapaḥ śaucaṁ kṣāntir ārjavam eva ca jñānaṁ vijñānam āstikyam brāhmaṇa-karma svabhāva-jam
Control of mind, control of senses, austerity, purity, forbearance, straightforwardness, knowledge, wisdom, and faith—these constitute the duty of brahmanas, born of their nature.
Krishna explains the duties of brahmanas. 'Śamo damas tapaḥ śaucaṁ kṣāntir ārjavam eva ca'—control of mind (śamaḥ), control of senses (damaḥ), austerity (tapaḥ), purity (śaucam), forbearance (kṣāntiḥ), straightforwardness (ārjavam). 'Jñānaṁ vijñānam āstikyam brāhmaṇa-karma svabhāva-jam'—knowledge (jñānam), wisdom (vijñānam), faith (āstikyam)—these constitute the duty of brahmanas (brāhmaṇa-karma), born of their nature (svabhāva-jam). These are sattvic duties: qualities of knowledge, wisdom, self-control, purity, and faith. Brahmanas are those whose nature inclines toward knowledge, teaching, contemplation, and spiritual guidance. Their duty is to cultivate wisdom, control their mind and senses, practice austerity, maintain purity, and have faith. This is not about birth—it's about natural qualities and inclinations.