SB 6.5.20

śāstrasya pitur ādeśaṁ
 yo na veda nivartakam
kathaṁ tad-anurūpāya
 guṇa-visrambhy upakramet
Word for word: 
śāstrasya — of the scriptures; pituḥ — of the father; ādeśam — the instruction; yaḥ — one who; na — not; veda — understands; nivartakam — which brings about the cessation of the material way of life; katham — how; tat-anurūpāya — to follow the instruction of the śāstras; guṇa-visrambhī — a person entangled in the three modes of material nature; upakramet — can engage in the creation of progeny.
Translation: 
[Nārada Muni had asked how one could ignorantly defy one’s own father. The Haryaśvas understood the meaning of this question.] One must accept the original instructions of the śāstra. According to Vedic civilization, one is offered a sacred thread as a sign of second birth. One takes his second birth by dint of having received instructions in the śāstra from a bona fide spiritual master. Therefore, śāstra, scripture, is the real father. All the śāstras instruct that one should end his material way of life. If one does not know the purpose of the father’s orders, the śāstras, he is ignorant. The words of a material father who endeavors to engage his son in material activities are not the real instructions of the father.
Purport: 

Bhagavad-gītā (16.7) says, pravṛttiṁ ca nivṛttiṁ ca janā na vidur āsurāḥ: demons, who are less than human beings but are not called animals, do not know the meaning of pravṛtti and nivṛtti, work to be done and work not to be done. In the material world, every living entity has a desire to lord it over the material world as much as possible. This is called pravṛtti-mārga. All the śāstras, however, advise nivṛtti-mārga, or release from the materialistic way of life. Apart from the śāstras of the Vedic civilization, which is the oldest of the world, other śāstras agree on this point. For example, in the Buddhist śāstras Lord Buddha advises that one achieve nirvāṇa by giving up the materialistic way of life. In the Bible, which is also śāstra, one will find the same advice: one should cease materialistic life and return to the kingdom of God. In any śāstra one may examine, especially the Vedic śāstra, the same advice is given: one should give up his materialistic life and return to his original, spiritual life. Śaṅkarācārya also propounds the same conclusion. Brahma satyaṁ jagan mithyā: this material world or materialistic life is simply illusion, and therefore one should stop his illusory activities and come to the platform of Brahman.

The word śāstra refers to the scriptures, particularly the Vedic books of knowledge. The VedasSāma, Yajur, Ṛg and Atharva — and any other books deriving knowledge from these Vedas are considered Vedic literatures. Bhagavad-gītā is the essence of all Vedic knowledge, and therefore it is the scripture whose instructions should be especially accepted. In this essence of all śāstras, Kṛṣṇa personally advises that one give up all other duties and surrender unto Him (sarva-dharmān parityajya mām ekaṁ śaraṇaṁ vraja).

One should be initiated into following the principles of śāstra. In offering initiation, our Kṛṣṇa consciousness movement asks one to come to the conclusion of śāstra by taking the advice of the supreme speaker of the śāstra, Kṛṣṇa, forgetting the principles of the materialistic way of life. Therefore the principles we advise are no illicit sex, no intoxication, no gambling and no meat-eating. These four types of engagement will enable an intelligent person to get free from the materialistic life and return home, back to Godhead.

In regard to the instructions of the father and mother, it may be said that every living entity, including even the insignificant cats, dogs and serpents, takes birth of a father and mother. Therefore, getting a material father and mother is not a problem. In every form of life, birth after birth, the living entity gets a father and mother. In human society, however, if one is satisfied with his material father and mother and their instructions and does not make further progress by accepting a spiritual master and being educated in the śāstras, he certainly remains in darkness. The material father and mother are important only if they are interested in educating their son to become free from the clutches of death. As instructed by Ṛṣabhadeva (Bhāg. 5.5.18): pitā na sa syāj jananī na sā syāt/ na mocayed yaḥ samupeta-mṛtyum. One should not strive to become a mother or father if one cannot save one’s dependent son from the impending danger of death. A parent who does not know how to save his son has no value because such fathers and mothers may be had in any form of life, even among the cats, dogs and so on. Only a father and mother who can elevate their son to the spiritual platform are bona fide parents. Therefore according to the Vedic system it is said, janmanā jāyate śūdraḥ: one is born of a material father and mother as a śūdra. The purpose of life, however, is to become a brāhmaṇa, a first-class man.

A first-class intelligent man is called a brāhmaṇa because he knows the Supreme Brahman, the Absolute Truth. According to the Vedic instructions, tad-vijñānārthaṁ sa gurum evābhigacchet: to know this science, one must approach a bona fide guru, a spiritual master who will initiate the disciple with the sacred thread so that he may understand the Vedic knowledge. Janmanā jāyate śūdraḥ saṁskārād dhi bhaved dvijaḥ. Becoming a brāhmaṇa through the endeavor of a bona fide spiritual master is called saṁskāra. After initiation, one is engaged in study of the śāstra, which teaches the student how to gain release from materialistic life and return home, back to Godhead.

The Kṛṣṇa consciousness movement is teaching this higher knowledge of retiring from materialistic life to return to Godhead, but unfortunately many parents are not very satisfied with this movement. Aside from the parents of our students, many businessmen are also dissatisfied because we teach our students to abandon intoxication, meat-eating, illicit sex and gambling. If the Kṛṣṇa consciousness movement spreads, the so-called businessmen will have to close their slaughterhouses, breweries and cigarette factories. Therefore they are also very much afraid. However, we have no alternative than to teach our disciples to free themselves from materialistic life. We must instruct them in the opposite of material life to save them from the repetition of birth and death.

Nārada Muni, therefore, advised the Haryaśvas, the sons of Prajāpati Dakṣa, that instead of begetting progeny, it would be better to leave and achieve the perfection of spiritual understanding according to the instructions of the śāstras. The importance of the śāstras is mentioned in Bhagavad-gītā (16.23):

yaḥ śāstra-vidhim utsṛjya
 vartate kāma-kārataḥ
na sa siddhim avāpnoti
 na sukhaṁ na parāṁ gatim

“One who disregards the injunctions of the śāstras and acts whimsically, as he likes, never achieves the perfection of life, not to speak of happiness. Nor does he return home to the spiritual world.”