The brahminical qualification is described in the Bhagavad-gītā: satyam śauca śama dama titikṣa ārjavam, jñānaṁ vijñānam āstikyaṁ brahma-karma svabhāva-jam (BG 18.42). Those who are actually Brāhmin, they must be truthful, always clean, inside and outside. Truthful, clean, and controlling the senses, śama dama, controlling the mind, controlling the senses, controlling the mind; śama dama titikṣa, tolerance, tolerance; ārjavam, simplicity; and jñānam, must be profoundly wise; vijñānam, practical application in life; jñānaṁ vijñānam āstikyam, full faith in scriptures and in God, or Kṛṣṇa, āstikyam. Brahma-karma svabhāva-jam: "These are natural duties, or work, of a Brāhmin."
And in the Bhagavad-gītā you will find in another place, cātur-varṇyaṁ mayā sṛṣṭaṁ guṇa-karma-vibhāgaśaḥ (BG 4.13). "These four classes of classification of the society, it is made by Me." That means this classification of society in the human society, that is made by God. What is that classification? The Brāhmin, the Kṣatriya, the Vaiśya and the Śūdra. It is not the name, but it is guṇa-karma. Brāhmin means quality and work, Kṣatriya means quality and work, and Vaiśya means quality and work. There is no question of birthright.
It is a false proposition that a Brāhmin's son becomes Brāhmin. No, not necessarily. If he properly becomes initiated under the guidance of a spiritual master, then he is Brāhmin. Otherwise, if he has acquired the qualities of a Śūdra, then he should be considered as a Śūdra. These are the śāstric injunctions. And this classification is all over the world. Don't think that it is Indian or Vedic system. No. In every country, in every place, in every planet, these four divisions are there.
Brāhmins means those who are interested in spiritual life, they are called Brāhmins, intelligent class. They are called intelligent class, because unless one is intelligent, he will simply consider that this body is he, identification of the body. That is foolishness. Brāhmins means brahma jānātīti brāhmaṇaḥ . . . one who knows that "I am ahaṁ brahmāsmi," and he has actually realized that "I am not this body; I am pure spirit self . . ." It is not the question of Hindu, Muslim. Anyone. Anyone who knows this knowledge that "I am the self," and acts in that way, is a Brāhmin.