Brāhmin means one who knows God. Brahma jānāti iti brāhmana. brāhmin is not by birth. So anyone who can understand what is God, he becomes brāhmin. The same example: anyone who is highly learned scholar and lawyer, he becomes a high court judge. Or if you see one high court judge, it is to be understood that he has passed all these. Similarly, brāhmin means one who knows God. Unless you know God, unless you know Kṛṣṇa, you cannot engage yourself fully, devoutly, in the service of the Lord. It is . . . Kṛṣṇa is unlimited. It is not possible to know Him fully. But svalpam apy asya dharmasya (BG 2.40): if you understand Him slightly—it is not possible to understand Him fully; slightly—then you become a brāhmin.
So brāhmin means there is no sinful activity. All your pious life. Satyaṁ śaucam . . . satyaṁ, śaucam, āstikyam, jñānaṁ, vijñānam, śamo, dama (SB 1.16.26)—these are the qualification. Satyaṁ means a brāhmin is truthful, and he's controlling the mind, he's controlling the senses. Śamo dama titikṣa: he's tolerant, and ārjavam, he's very simple. Life is very simple. Jñānaṁ—full of knowledge; vijñānaṁ—practical application of knowledge in life; and āstikyam—believer, not unbeliever; believer in the existence of God. These are the qualification of brāhmin.