The śāstra enjoins that even if good qualifications are seen in a person born in a family other than that of a brāhmaṇa, the qualified man has to be accepted as a brāhmaṇa, and similarly if a person born in the family of a brāhmaṇa is void ofbrahminical qualification, then he must be treated as a non-brāhmaṇa or, in better terms, a relative of a brāhmaṇa. Lord Śrī Kṛṣṇa, the supreme authority of all religious principles, the Vedas, has personally pointed out these differences, and He is about to explain the reason for this in the following ślokas.
(Srimad Bhagavatam-----1:7:35-----purport).

There is a stricture that no one should try to learn the Vedas who is not a qualified brāhmaṇa. This stricture has been wrongly interpreted in so many ways. A class of men, who claim brahminical qualification simply by their birthright in the family of a brāhmaṇa, claim that the study of the Vedas is a monopoly of the brāhmaṇa caste only.
(Srimad Bhagavatam-----1:4:24-----purport).

Money given in charity to a suitable person is guaranteed bank balance in the next life. Such charity is recommended to be given to a brāhmaṇa. If the money is given in charity to a non-brāhmaṇa (without brahminical qualification) the money is returned in the next life in the same proportion. If it is given in charity to a half-educated brāhmaṇa, even then the money is returned double. If the money is given in charity to a learned and fully qualified brāhmaṇa, the money is returned a hundred and a thousand times, and if the money is given to a veda-pāraga (one who has factually realized the path of the Vedas), it is returned by unlimited multiplication.
(Srimad Bhagavatam-----2:3:17-----purport).

When the brāhmaṇa class or caste gradually became easygoing, being fed by the society although they had no brahminical qualifications, they degraded themselves into brahma-bandhus, or disqualified brāhmaṇas, and thus other members of society also gradually fell down from the social standard of progressive life. As described in Bhagavad-gītā, the caste system is the creation of the Lord and is arranged according to the quality of work rendered to society and not in terms of birthright, as falsely claimed in the present degraded society.
(Srimad Bhagavatam-----3:3:27-----purport).

A brāhmaṇa is one who has understood Brahman, and a Vaiṣṇava is one who has understood the Personality of Godhead. Brahman realization is the beginning of realization of the Personality of Godhead. One who understands the Personality of Godhead also knows the impersonal feature of the Supreme, which is Brahman. Therefore one who becomes a Vaiṣṇava is already a brāhmaṇa. It should be noted that the glories of the brāhmaṇa described in this chapter by the Lord Himself refer to His devotee-brāhmaṇa, or the Vaiṣṇava. It should never be misunderstood that the so-called brāhmaṇas who are born in brāhmaṇa families but have no brahminical qualifications are referred to in this connection.
(Srimad Bhagavatam-----3:16:4-----purport).

A śūdra is forbidden to take lessons from the Vedas because a śūdra, due to his unclean habits, is not worthy to hear such instructions. This restriction, that unless one has acquired the brahminical qualifications one should not read the Vedic literatures, is like the restriction that a law student should not enter a law college unless he has been graduated from all lower grades.
(Srimad Bhagavatam-----4:2:13-----purport).

In the age of Kali, taking advantage of the fact that by feeding a brāhmaṇa one obtains a more effective result than by performing sacrifices, a class of men with nobrahminical qualifications claim the eating privilege known as brāhmaṇa-bhojana simply on the basis of their birth in brāhmaṇa families.
(Srimad Bhagavatam-----4:21:42-----purport).

As Śrī Prahlāda Mahārāja said:
viprād dviṣaḍ-guṇa-yutād aravinda-nābha-
pādāravinda-vimukhāc chvapacaṁ variṣṭham
(S.B.7:9:10)
Even if one is a brāhmaṇa and is qualified with all the brahminical qualifications, he is considered degraded if he is averse to worshiping the Supreme Personality of Godhead. But if a person is attached to the service of the Lord, he becomes glorified even if he is born in a caṇḍāla family.
(Srimad Bhagavatam-----4:31:10-----purport).

Nārada Muni says:
yasya yal lakṣaṇaṁ proktaṁ
puṁso varṇābhivyañjakam
yad anyatrāpi dṛśyeta
tat tenaiva vinirdiśet
(S.B.7:11:35)
It is not a fact that because one is born in a brāhmaṇa family he is automatically a brāhmaṇa. He has a better chance to become a brāhmaṇa, but unless he meets all the brahminical qualifications, he cannot be accepted as such. On the other hand, if the brahminical qualifications are found in the person of a śūdra, he should immediately be accepted as a brāhmaṇa. To substantiate this there are many quotations from Bhāgavatam, Mahābhārata, Bharadvāja-saṁhitā and the pañcarātra, as well as many other scriptures.
(Srimad Bhagavatam-----4:31:10-----purport).

Tamo-guṇa and rajo-guṇa increase lust and greed, which implicate a living entity in such a way that he must exist in this material world in many, many forms. That is very dangerous. One should therefore be brought to sattva-guṇa by the establishment of varṇāśrama-dharma and should develop the brahminical qualifications of being very neat and clean, rising early in the morning and seeing maṅgala-ārātrika, and so on. In this way, one should stay in sattva-guṇa, and then one cannot be influenced by tamo-guṇa and rajo-guṇa.
(Srimad Bhagavatam-----10:13:53-----purport).

Brahmaṇya means one who fully possesses the brahminical qualifications, which are said to be as follows: truthfulness, self-control, purity, mastery of the senses, simplicity, full knowledge by practical application, and engagement in devotional service. Lord Kṛṣṇa possesses all these qualities, and He is worshiped by persons who themselves possess such qualities. There are thousands and millions of names of Lord Kṛṣṇa—Viṣṇu-sahasra-nāma—and all of them are given to Him because of His transcendental qualities.
(Krsna Book).

When one attains brahminical qualifications, he becomes happy and enthusiastic to render devotional service to the Lord. Automatically the science of God is unveiled before him. By knowing the science of God, one gradually becomes freed from material attachments, and one's doubtful mind becomes crystal clear by the grace of the Lord. One who attains this stage is a liberated soul and can see the Lord in every step of life. This is the perfection of sambhava, as described in this mantra of Śrī Īśopaniṣad.
(Sri Isopanishad).