Nārada Muni says, yad anyatrāpi dṛśyeta tat tenaiva vinirdiśet (SB 7.11.35). Every has got qualification. That is very natural. That is very natural. Yasya hi yal-lakṣaṇaṁ syād varṇābhivyanjakam (SB 7.11.35). To ascertain which class a man belongs, whether he is a brāhmaṇa or a kṣatriya or vaiśya, there are qualifications. Just like ordinarily we know, we understand an engineer by qualification, a medical practitioner by qualification. We don't ask, "Whose son you are, Mr. Engineer?" No. If you have got engineer's qualification, you are engineer. Otherwise, how can you be engineer? Similarly, yasya hi yal-lakṣaṇaṁ syād varṇābhivyanjakam. Varṇa. This is brahminical quality.
In Bhagavad-gītā it is said, satyaḥ śamo damas titikṣaḥ arjavam. Sauryaṁ tejo yuddhe cāpy apālayanam (BG 18.43)—kṣatriya. Kṣatriya must be very heroic. He'll never go away from fighting. If a kṣatriya is challenged, "I want to fight with you," "Yes, come on." That is kṣatriya. Similarly, brāhmaṇa. These are qualifications. So if such qualification is acquired by somebody else, even though he's not born in that family, Nārada Muni says, tat tenaiva vinirdiśet (SB 7.11.35). If a brāhmaṇa has not acquired the brahminical qualifications but a kṣatriya qualification or a vaiśya qualification or a śūdra qualification, then, according to the quality, guṇa, and work, he should be ascertained. Similarly, others also. Yad anyatrāpi dṛśyeta (SB 7.11.35). This is śāstric injunction. And Kṛṣṇa therefore refers to brahma-sūtra padaiś caiva hetumadbhir viniścitaiḥ (BG 13.5). So we have to accept the Vedānta-sūtra, knowledge, through Vedānta-sūtra. Śrīla Jīva Gosvāmī says knowledge means veda-jñāna. Vedānta-sūtra jñāna, that is knowledge. Because it is very reasonably stated. Reasonably. Hetumadbhir viniścitaiḥ.