Viśvanātha Cakravartī Ṭhākura explains the position of brāhmaṇas and kṣatriyas as follows. Brāhmaṇas have six occupational duties, of which three are compulsory—namely, studying the Vedas, worshiping the Deity and giving charity. By teaching, by inducing others to worship the Deity, and by accepting gifts, the brāhmaṇas receive the necessities of life. This is also confirmed in the Manu-saṁhitā:
ṣaṇṇāṁ tu karmaṇām asya
trīṇi karmāṇi jīvikā
yajanādhyāpane caiva
viśuddhāc ca pratigrahaḥ
Of the six occupational duties of the brāhmaṇas, three are compulsory—namely, worship of the Deity, study of the Vedas and the giving of charity. In exchange, a brāhmaṇa should receive charity, and this should be his means of livelihood. A brāhmaṇa cannot take up any professional occupational duty for his livelihood. The śāstras especially stress that if one claims to be abrāhmaṇa, he cannot engage in the service of anyone else; otherwise he at once falls from his position and becomes a śūdra. Śrīla Rūpa Gosvāmī and Sanātana Gosvāmī belonged to a very respectful family, but because they engaged in the service of Nawab Hussain Shah—not even as ordinary clerks, but as ministers—they were ostracized from brahminical society. Indeed, they became like Mohammedans and even changed their names. Unless a brāhmaṇa is very pure, he cannot accept charity from others. Charity should be given to those who are pure. Even if one is born in a family of brāhmaṇas, if one acts as a śūdra one cannot accept charity, for this is strictly prohibited.
(Srimad Bhagavatam-----7:11:14-----purport).

The occupational duty of a brāhmaṇa should not be accepted by persons in lower social orders, especially vaiśyas and śūdras. For example, an occupational duty of the brāhmaṇa is to teach Vedic knowledge, but unless there is an emergency, this professional duty should not be accepted by the kṣatriyas, vaiśyas or śūdras. Even a kṣatriya cannot accept the duties of a brāhmaṇa unless there is an emergency, and then even if he does so he should not accept charity from anyone else. Sometimes brāhmaṇas protest against our Kṛṣṇa consciousness movement for creating brāhmaṇas from Europeans, or, in other words, from mlecchas and yavanas. This movement, however, is here supported in Śrīmad-Bhāgavatam. At the present moment, society is in a chaotic condition, and everyone has given up the cultivation of spiritual life, which is especially meant for the brāhmaṇas. Because spiritual culture has been stopped all over the world, there is now an emergency, and therefore it is now time to train those who are considered lower and condemned, so that they may become brāhmaṇasand take up the work of spiritual progress. The spiritual progress of human society has been stopped, and this should be considered an emergency. Here is solid support from Nārada Muni of the movement known as Kṛṣṇa consciousness.
(Srimad Bhagavatam-----7:11:17-----purport).

As for economic development, the responsibility for this should be entrusted mainly to the vaiśyas and gṛhasthas. Human society should be divided into varṇas and āśramas-brāhmaṇa, kṣatriya, vaiśya, śūdra, brahmacarya, gṛhastha, vānaprastha and sannyāsa. Economic development is necessary for gṛhasthas. Brāhmaṇa gṛhasthas should be satisfied with a life of adhyayana, adhyāpana, yajana and yājana—being learned scholars, teaching others to be scholars, learning how to worship the Supreme Personality of Godhead, Viṣṇu, and also teaching others how to worship Lord Viṣṇu, or even the demigods. A brāhmaṇa should do this without remuneration, but he is allowed to accept charity from a person whom heteaches how to be a human being.
(Srimad Bhagavatam-----7:14:10-----purport).

The words bhikṣor mārga, "the path of the renounced order," are very significant in this regard. A sannyāsī is called tridaṇḍi-bhikṣu because his duty is to beg alms from the homes of gṛhasthas and to give the gṛhasthas spiritual instructions. A sannyāsī is allowed to beg from door to door, but a gṛhastha cannot do so. Gṛhasthas may earn their living according to the four divisions of spiritual life. A brāhmaṇa gṛhastha may earn his livelihood by becoming a learned scholar and teaching people in general how to worship the Supreme Personality of Godhead. He may also assume the duty of worship himself. Therefore it is said that only brāhmaṇas may engage in Deity worship, and they may accept as prasāda whatever people offer the Deity. Although a brāhmaṇa may sometimes accept charity, it is not for his personal maintenance but for the worship of the Deity. Thus a brāhmaṇa does not stock anything for his future use.
(Srimad Bhagavatam-----6:5:36-----purport).

It is said, vṛddhatvaṁ vayasā vinā: one may be senior without being advanced in age. Even if one is not old, one gains seniority if he is senior in knowledge. Viśvarūpa was junior in relationship to the demigods because he was their nephew, but the demigods wanted to accept him as their priest, and therefore he would have to accept obeisances from them. The demigods explained that this should not be a cause for hesitation; he could become their priest because he was advanced in Vedic knowledge. Similarly. Cāṇakya Paṇḍita advises, nīcād apy uttamaṁ jñānam: one may accept education from a member of a lower social order. The brāhmaṇas, the members of the most elevated varṇa, are teachers, but a person in a lower family, such as a family of kṣatriyas, vaiśyas or even śūdras, may be accepted as a teacher if he has knowledge. Śrī Caitanya Mahāprabhu approved of this when He expressed this opinion before Rāmānanda Rāya (CC.2:8:128):
kibā vipra, kibā nyāsī, śūdra kene naya
yei kṛṣṇa-tattva-vettā, sei 'guru' haya
It does not matter whether one is a brāhmaṇa, śūdra, gṛhastha or sannyāsī. These are all material designations. A spiritually advanced person has nothing to do with such designations. Therefore, if one is advanced in the science of Kṛṣṇa consciousness, regardless of his position in human society, he may become a spiritual master.
(Srimad Bhagavatam-----6:7:33-----purport).

Since there must always be a difference of opinion between demons and devotees, Hiraṇyakaśipu, when criticized by his son Prahlāda Mahārāja, should not have been surprised that Prahlāda Mahārāja differed from his way of life. Nonetheless, Hiraṇyakaśipu was extremely angry and wanted to rebuke his son for deriding his teacher or spiritual master, who had been born in the brāhmaṇa family of the great ācārya Śukrācārya. The word śukra means "semen," and ācārya refers to a teacher or guru. Hereditary gurus, or spiritual masters, have been accepted everywhere since time immemorial, but Prahlāda Mahārāja declined to accept such a seminal guru or take instruction from him. An actual guru is śrotriya, one who has heard or received perfect knowledge through paramparā, the disciplic succession. Therefore Prahlāda Mahārāja did not recognize a seminal spiritual master. Such spiritual masters are not at all interested in Viṣṇu. Indeed, they are hopeful of material success (bahir-artha-māninaḥ). The word bahiḥ means "external," artha means "interest," and mānina means "taking very seriously."
(Srimad Bhagavatam-----7:5:31-----purport).

Aśvatthāmā was condemned by the Lord Himself, and he was treated by Arjuna just like a culprit, not like the son of a brāhmaṇa or teacher. But when he was brought before Śrīmatī Draupadī, she, although begrieved for the murder of her sons, and although the murderer was present before her, could not withdraw the due respect generally offered to a brāhmaṇa or to the son of abrāhmaṇa. This is due to her mild nature as a woman. Women as a class are no better than boys, and therefore they have no discriminatory power like that of a man. Aśvatthāmā proved himself to be an unworthy son of Droṇācārya or of a brāhmaṇa, and for this reason he was condemned by the greatest authority, Lord Śrī Kṛṣṇa, and yet a mild woman could not withdraw her natural courtesy for a brāhmaṇa.
(Srimad Bhagavatam-----1:7:42-----purport).

As soon as Aśvatthāmā was brought before Draupadī, she thought it intolerable that a brāhmaṇa should be arrested like a culprit and brought before her in that condition, especially when the brāhmaṇa happened to be a teacher's son.
Arjuna arrested Aśvatthāmā knowing perfectly well that he was the son of Droṇācārya. Kṛṣṇa also knew him to be so, but both of them condemned the murderer without consideration of his being the son of a brāhmaṇa. According to revealed scriptures, a teacher or spiritual master is liable to be rejected if he proves himself unworthy of the position of a guru or spiritual master. A guru is called also an ācārya, or a person who has personally assimilated all the essence of śāstras and has helped his disciples to adopt the ways. Aśvatthāmā failed to discharge the duties of a brāhmaṇa or teacher, and therefore he was liable to be rejected from the exalted position of a brāhmaṇa. On this consideration, both Lord Śrī Kṛṣṇa and Arjuna were right in condemning Aśvatthāmā. But to a good lady like Draupadī, the matter was considered not from the angle of śāstric vision, but as a matter of custom. By custom, Aśvatthāmā was offered the same respect as offered to his father. It was so because generally the people accept the son of a brāhmaṇa as a real brāhmaṇa, by sentiment only. Factually the matter is different. A brāhmaṇa is accepted on the merit of qualification and not on the merit of simply being the son of a brāhmaṇa.
(Srimad Bhagavatam-----1:7:43-----purport).

Dhanur-veda, or military science, was taught by Droṇācārya with all its confidential secrets of throwing and controlling by Vedic hymns. Gross military science is dependent on material weapons, but finer than that is the art of throwing the arrows saturated with Vedic hymns, which act more effectively than gross material weapons like machine guns or atomic bombs. The control is by Vedic mantras, or the transcendental science of sound. It is said in the Rāmāyaṇa that Mahārāja Daśaratha, the father of Lord Śrī Rāma, used to control arrows by sound only. He could pierce his target with his arrow by only hearing the sound, without seeing the object. So this is a finer military science than that of the gross material military weapons used nowadays. Arjuna was taught all this, and therefore Draupadī wished that Arjuna feel obliged to Ācārya Droṇa for all these benefits. And in the absence of Droṇācārya, his son was his representative. That was the opinion of the good lady Draupadī. It may be argued why Droṇācārya, a rigid brāhmaṇa, should be a teacher in military science. But the reply is that a brāhmaṇa should become a teacher, regardless of what his department of knowledge is. A learned brāhmaṇa should become a teacher, a priest and a recipient of charity. A bona fide brāhmaṇa is authorized to accept such professions.
(Srimad Bhagavatam-----1:7:44-----purport).

A real brāhmaṇa is the natural teacher or spiritual master. Unless one has Vedic knowledge, one cannot become a spiritual master. The perfect knowledge of the Vedas is to know the Lord, the Personality of Godhead, and that is the end of Vedic knowledge, or Vedānta. One who is situated in the impersonal Brahman and has no information of the Supreme Personality of Godhead may become a brāhmaṇa, but he cannot become a spiritual master. It is said in the Padma Purāṇa:
ṣaṭ-karma-nipuṇo vipro
mantra-tantra-viśāradaḥ
avaiṣṇavo gurur na syād
vaiṣṇavaḥ śva-paco guruḥ
An impersonalist can become a qualified brāhmaṇa, but he cannot become a spiritual master unless and until he is promoted to the stage of a Vaiṣṇava, or a devotee of the Personality of Godhead.
(Srimad Bhagavatam-----3:6:30-----purport).

The vaiśyas are divided into many subsections: some of them are called kṣetrī, or landowners, some are called kṛṣaṇa, or land tillers, some of them are called tila-vaṇik, or grain raisers, some are called gandha-vaṇik, or merchants in spices, and some are called suvarṇa-vaṇik, or merchants in gold and banking. The brāhmaṇas are the teachers and spiritual masters, the kṣatriyas protect the citizens from the hands of thieves and miscreants, and the vaiśyas are in charge of production and distribution. The śūdras, the unintelligent class of men who cannot act independently in any of the above-mentioned activities, are meant for serving the three higher classes for their livelihood.
(Srimad Bhagavatam-----3:6:32-----purport).

One who actually assimilated the essence of the Vedas can preach the truth. He is compassionate to conditioned souls who are suffering the threefold miseries of this conditional world due to their not being Kṛṣṇa conscious. A brāhmaṇa should take pity on the people and preach Kṛṣṇa consciousness in order to elevate them. Śrī Kṛṣṇa Himself, the Supreme Personality of Godhead, personally descends into this universe from the spiritual kingdom to teach conditioned souls about the values of spiritual life. He tries to induce them to surrender unto Him. Similarly, the brāhmaṇas do the same thing. After assimilating the Vedic instructions, they assist the Supreme Lord in His endeavor to deliver conditioned souls. The brāhmaṇas are very dear to the Supreme Lord due to their high sattva-guṇa qualities, and they also engage in welfare activities for all conditioned souls in the material world.
(Srimad Bhagavatam-----5:5:24-----purport).

Tasmād guruṁ prapadyeta jijñāsuḥ śreya uttamam: (S.B.11:3:21) one who is very interested in understanding the activities in the spiritual world must search out a guru—a bona fide representative of Kṛṣṇa. From all angles of vision, therefore, the word guru is especially meant for the bona fide representative of Kṛṣṇa and no one else. Padma Purāṇa states, avaiṣṇavo gurur na syāt: one who is not a Vaiṣṇava, or who is not a representative of Kṛṣṇa, cannot be a guru. Even the most qualified brāhmaṇa cannot become a guru if he is not a representative of Kṛṣṇa. Brāhmaṇas are supposed to acquire six kinds of auspicious qualifications: they become very learned scholars (paṭhana) and very qualified teachers (pāṭhana); they become expert in worshiping the Lord or the demigods (yajana), and they teach others how to execute this worship (yājana); they qualify themselves as bona fide persons to receive alms from others (pratigraha), and they distribute the wealth in charity (dāna). Yet even a brāhmaṇa possessing these qualifications cannot become a guru unless he is the representative of Kṛṣṇa (gurur na syāt). Vaiṣṇavaḥ śva-paco guruḥ: but a Vaiṣṇava, a bona fide representative of the Supreme Personality of Godhead, Viṣṇu, can become a guru, even if he is śva-paca, a member of a family of dog-eaters.
(Srimad Bhagavatam-----5:17:11-----purport).