aśāstra-vihitaḿ ghoraḿ
tapyante ye tapo janāḥ

karṣayantaḥ śarīra-sthaḿ
bhūta-grāmam acetasaḥ
māḿ caivāntaḥ śarīra-sthaḿ
tān viddhy āsura-niścayān

Translation of Bhagavad Gita 17.5-6

Those who undergo severe austerities and penances not recommended in the scriptures, performing them out of pride and egoism, who are impelled by lust and attachment, who are foolish and who torture the material elements of the body as well as the Supersoul dwelling within, are to be known as demons.

Commentary by Sri A.C. Bhaktivedanta Swami Prabhupada of Gaudiya Sampradaya:

There are persons who manufacture modes of austerity and penance which are not mentioned in the scriptural injunctions. For instance, fasting for some ulterior purpose, such as to promote a purely political end, is not mentioned in the scriptural directions. The scriptures recommend fasting for spiritual advancement, not for some political end or social purpose. Persons who take to such austerities are, according to Bhagavad-gita, certainly demoniac. Their acts are against the scriptural injunctions and are not beneficial for the people in general. Actually, they act out of pride, false ego, lust and attachment for material enjoyment. By such activities, not only is the combination of material elements of which the body is constructed disturbed, but also the Supreme Personality of Godhead Himself living within the body.

Such unauthorized fasting or austerities for some political end are certainly very disturbing to others. They are not mentioned in the Vedic literature. A demoniac person may think that he can force his enemy or other parties to comply with his desire by this method, but sometimes one dies by such fasting. These acts are not approved by the Supreme Personality of Godhead, and He says that those who engage in them are demons. Such demonstrations are insults to the Supreme Personality of Godhead because they are enacted in disobedience to the Vedic scriptural injunctions. The word acetasah is significant in this connection. Persons of normal mental condition must obey the scriptural injunctions. Those who are not in such a position neglect and disobey the scriptures and manufacture their own way of austerities and penances. One should always remember the ultimate end of the demoniac people, as described in the previous chapter.

The Lord forces them to take birth in the wombs of demoniac persons. Consequently they will live by demoniac principles life after life without knowing their relationship with the Supreme Personality of Godhead. If, however, such persons are fortunate enough to be guided by a spiritual master who can direct them to the path of Vedic wisdom, they can get out of this entanglement and ultimately achieve the supreme goal.

Commentary by Sri Vishvanatha Chakravarthi Thakur of Gaudiya Sampradaya:

“You asked the question ‘What is the position of those who, giving up the rules of scripture but with faith, without enjoyment of objects, perform worship?’ Now hear the answer.” The Lord answers in two verses.

They perform austerities which are harmful to living entities (ghoram). The mention of austerities is representative of other acts such a japa and sacrifice as well. They perform all these acts against the rules of scriptures. The absence of desire for enjoyment and being filled with faith (sraddhanvitah) are understood in this context. They are endowed with ostentation (dambhah) and pride (ahamkarah) because without those two, they could not transgress the rules of scripture. They also have desire for eternal youth, eternal life, kingdom and such things (kama), attachment to their particular austerity (raga), and ability to perform the austerity (bala), like that Hiranyakasipu and others. Endowed with these qualities, they starve or cause suffering (karsyantah) to all elements such as earth (bhuta gramam), to me (mam) and to my amsa the jiva, situated in their bodies. Know these people to be also situated on the level of asuras.

Commentary by Sri Ramanuja of Sri Sampradaya:

17.5 – 17.6 ‘Those men who perform terrible pernances not enjoined by the Sastras’ — this is illustrative of sacrifices etc., of a similar nature. Those who perform sacrifices, etc., sacrifices which are not enjoined by the Sastras and demand much exertion, those who are possessed of ‘ostentation and conceit and are goaded by sensual desire, attachment and passion’ — they torture the group of elements such as earth etc., in their bodies. They also torture the individual self which is a part of Myself and is within their bodies. Those who perform such sacrifices etc., know them to be demoniacal in their resolves. The resolve of demons is demoniac resolve. The demons are those who act contrary to My commandments. Since they act contrary to My commandments, they do not have even a iota of joy, but as stated earlier, they fall a prey to a multitude of calamities. ‘They fall into a foul Naraka’ (16.16). Now, Sri Krsna, resuming the subject, details the differences according to the Gunas with reference to sacrifice, etc., enjoined by the Sastras. To begin with, he describes three kinds of food, since the growth of Sattva etc., has its source in food, as Srutis declare thus: ‘For my dear, the mind consists of food’ (Cha. U., 6.5.4) and ‘when the food is pure, the man becomes pure’ (Cha. U., 7.26.2).

Commentary by Sri Sridhara Swami of Rudra Sampradaya:

Further incriminations regarding those situated in raja guna and tama guna or the mode of passion and the mode of ignorance respectively are given here. Some jivas or embodied beings who know nothing about the Vedic scriptures are anyway endowed with the divine nature and situated in sattva guna the mode of goodness right from birth. This is due to having been attracted to spiritual activities and righteousness in previous lives. The impressions from those lifetimes gave the impetus towards the divine nature and the opportunity in the present life to attain the association of the devotees of the Supreme Lord Krishna.

Others of mediocre nature in raja guna and of inferior nature in tama guna with deluded and depraved faith are extremely unfortunate. They follow pagan, heretical practices and rituals symbolising and involving blood sacrifices. They commit heinous, inerasable sins such as the slaughter of cows for which there is no atonement for. They commit cruel human sacrifices and blood drinking in their diabolical and depraved cravings and lust for power. They execute terrible inhuman deeds that are an aberration to creation. Degrading themselves and the atma or immortal soul existing within their own body and within the bodies of others. Know them to be without a doubt endowed with the demoniac nature. Without any discrimination they masochistically and sadistically execute extreme and painful rituals in their demented desire to surpass mortality. Yet they must perish and die anyway and because they executed such cruel and inhuman deeds which transgressed the ordinances and injunctions of the Vedic scriptures as well as engaging in prohibitive activities without any compunction they will be forced to suffer the full consequences of their sinful misdeeds and flagrant improprieties in hell.

Commentary by Sri Madhvacharya of Brahma Sampradaya:

The Anabhimian scripture states that those unfortunate jivas or embodied beings who oppress and chastise the Resplendent Supreme Lord who dwells within as Paramatma the supreme soul which resides within the etheric heart of every living entity in existence are of miniscule consciousness with meager perception. Thus without the vision of perception they oppress Him within their hearts and the hearts of others. The word asura means without light and is in general referred to those of the demoniac nature. Those who are void of light are void of light perception and also void of the light of perceptivity. The Agniveshya scripture states that those endowed with the divine nature are exclusively in sattva guna or the mode of goodness and study the Vedic scriptures and are receptive to Lord Krishna. While those that are of the demoniac nature are a combination of raja guna or mode of passion and tama guna or mode of ignorance and they never study the Vedic scriptures and even if by chance they get an opportunity to hear from them they cannot fathom the values contained therein because they are inimical to the Supreme Lord.

Commentary by Sri Keshava Kashmiri of Kumara Sampradaya:

The ignorant who indifferently disregard the Vedic scriptures while performing their own religious rituals with faith will find such faith divided into one of the three gunas or modes of material nature as well. The gunas known as sattva guna, raja guna and tama guna correspond to the modes of goodness, passion and ignorance respectively. But because they disrespect the ordinances and injunctions of the Vedic scriptures they must be excluded from those who are endowed with the divine nature and are thus unqualified for all four goals of human development which are artha or wealth, kama or pleasure, dharma or spiritual development and moksa or liberation from material existence. They are only qualified for two artha and kama; yet due to having some faith and piety they cannot be categorised as those possessing demoniac qualities; but neither can they be considered as endowed with divine qualities.

To clarify this discrepancy Lord Krishna will now answer what is the position of those such as these with misplaced faith due to ignorance of the absolute authority of the Vedic scriptures. Those who practice extreme vows of self deprecation such as emaciating fasting, masochistic flagellation, sadistic tormenting of the physical body, etc. all of which are not enjoined and sanctioned by the Vedic scriptures; simply enact them out of ostentation and egoism out of delusion in an attempt for perverse material gains. Abusing and torturing the physical body containing the atma or immortal soul, they disrespect themselves and the Supreme Lord as well who abides therein and cause the atma to enter lower and lower degraded species of existence where misery and suffering are unending. Know that such living entities possess the demoniac nature and should be vigilantly avoided by all means because they flagrantly disobey the commands of the Supreme Lord by disregarding the Vedic scriptures. Because the demoniac transgress the Vedic scriptures wilfully and even spitefully they never can obtain lasting happiness because they constantly engage in activities antagonistic to the Supreme Lord. Instead they fall into the foulest and excruciating of hells to suffer interminably.

Commentary by Sri Adi Shankaracharya of Advaita Sampradaya:

17.5 Ye, those; janah, persons; who tapyante, undertake, perform; ghoram, severe; tapah, austerity, productive of pain to oneself as also to creatures; asastra-vihitam, not sanctioned by the scriptures; they, being dambh-ahankara-samyuktah, given to ostentation and pride; and kama-raga-bala-anvitah, impelled by the strength of passion and attachment, or possessed of passion, attachment and strength [Kama-raga can also mean desirable objects and the desire to enjoy them.]-.

Commentary by Sri Abhinavagupta of Kaula Tantra Sampradaya:

17.4-6 Yajante etc., upto asura-niscayan. Unintelligently : i.e. due to their lack of discrimination. Emaciating Me too : Because they do not follow the purport of the scriptures. That is why they undertake practising austerities invented by their own intellect and they are rather men of the Tamas (Strand). Like faith, the food also is of three types, differentiated by the Sattva etc., so are the sacrifice, austerity and charity. That is being detailed as :

Sanskrit Shloka Without Transliteration Marks:

asastra-vihitam ghoram
tapyante ye tapo janah

karsayantah sarira-stham
bhuta-gramam acetasah
mam caivantah sarira-stham
tan viddhy asura-niscayan

Sanskrit to English Word for Word Meanings:

aśāstra — not in the scriptures; vihitam — directed; ghoram — harmful to others; tapyante — undergo; ye — those who; tapaḥ — austerities; janāḥ — persons; dambha — with pride; ahańkāra — and egoism; saḿyuktāḥ — engaged; kāma — of lust; rāga — and attachment; bala — by the force; anvitāḥ — impelled; karṣayantaḥ — tormenting; śarīra-stham — situated within the body; bhūta-grāmam — the combination of material elements; acetasaḥ — having a misled mentality; mām — Me; ca — also; eva — certainly; antaḥ — within; śarīra-stham — situated in the body; tān — them; viddhi — understand; āsura-niścayān — demons.