"Hearing and chanting about the transcendental holy name, form, qualities, paraphernalia, and pastimes of Lord Visnu, remembering these, serving the lotus feet of the Lord, offering the Lord respectful worship, offering prayers to the Lord, becoming His servant, considering the Lord one's best friend, and surrendering everything to Him--these are the nine processes of pure devotional service."
In order to take up these processes seriously, one must accept the regulative principles for spiritual life: no meat-eating, no illicit sex, no intoxication, and no gambling. Then one will be able to accept the injunction to chant the Hare Krsna maha-mantra and always be engaged in the service of the Lord in one of the above nine ways. If we accept this authority, our life will be successful, both spiritually and materially. Otherwise, we will have to be satisfied with indulging in sense gratification, performing sinful activities, suffering like dogs and hogs, and enduring repeated birth, old age, disease, and death."
A Second Chance, Chapter 9
"How a living entity becomes a victim of the material condition is lucidly explained in this verse. The beginning is to misidentify the body as one's self. Therefore Bhagavad-gita begins with the spiritual instruction that one is not the body, but is within the body. This consciousness can be possible only if one chants the holy name of Krsna, the Hare Krsna maha-mantra, and always keeps oneself in the association of devotees. This is the secret of success. Therefore we stress that one should chant the holy name of the Lord and keep oneself free from the contaminations of this material world, especially the contaminations of lusty desires for illicit sex, meat-eating, intoxication and gambling. With determination, one should vow to follow these principles and thus be saved from the miserable condition of material existence. The first necessity is to become freed from the bodily concept of life."
Srimad-Bhagavatam 6:2:38 Purport
"When the modes of passion and ignorance increase in human society, giving rise to unnecessary economic development, the result is that people become involved with wine, women and gambling. Then, being mad, they maintain big slaughterhouses or occasionally go on pleasure excursions to kill animals. Forgetting that however one may try to maintain the body, the body is subject to birth, death, old age and disease, such foolish rascals engage in sinful activities, one after another. Being duskrtis, they completely forget the existence of the supreme controller, who is sitting within the core of everyone's heart (isvarah sarva-bhutanam hrd-dese 'rjuna tisthati). That supreme controller is observing every bit of one's activity, and He rewards or punishes everyone by giving one a suitable body made by material nature (bhramayan sarva-bhutani yantrarudhani mayaya). In this way, sinful persons automatically receive punishment in different types of bodies. The root cause of this punishment is that when one unnecessarily accumulates wealth, one becomes more and more degraded, not knowing that his wealth will be finished with his next birth."
Srimad-Bhagavatam 10:10:9 Purport
"As mentioned before, there are four basic characteristics of an impure life--illicit sex, intoxication, meat-eating and gambling. According to the Vedic principles, sex should not be indulged in outside of marriage. In human society there is therefore a system of marriage which distinguishes us from the cats and dogs. Whether we are Hindu, Moslem, or Christian, we acknowledge the system of marriage. The purpose of this system is to avoid illicit sex. According to the Vedic system, intoxication is also discouraged; nor is meat-eating advocated, for human beings should be nonviolent. We have been given sufficient grains, fruits, milk, and vegetables, and there is no necessity to kill poor animals. Some people argue that if we do not eat meat we will be undernourished, but we can see that the students of this Krsna consciousness movement have given up meat and are very healthy, whereas people who are eating meat are still, despite their meat-eating, subject to so many diseases and unhealthy conditions. Gambling is also discouraged because it simply agitates the mind.
This then is the purificatory process by which one can become a brahmana. This path is open to everyone. A brahmana is one who is truthful and pure, tolerant and simple, full of knowledge and faith in God. He can control his mind and his senses also. At the present moment there is a great necessity for brahmanas, because almost everyone is a sudra, for almost everyone is wholly engaged in maintaining the body, eating, sleeping, mating and defending--all symptoms of animals and sudras."
Elevation to Krsna Consciousness, Chapter 3
"Whether we acted piously in this life or a previous life really doesn't matter. This chanting of Hare Krsna is so potent that through it we will immediately be purified. We should have the determination, however, not to become implicated in further impious activities. Therefore, for those who want to be initiated in this Society for Krsna consciousness, there are four principles: no illicit sex, no intoxication, no meat-eating, and no gambling. We don't say, "No sex." But we do say, "No illicit sex." If you want sex, get married and have Krsna conscious children. "No intoxication" means not even taking tea or coffee--to say nothing of other intoxicants. And there is no gambling and no meat-eating (including fish and eggs). Simply by following these four basic rules and regulations, one becomes immediately uncontaminated. No further endeavor is necessary. As soon as one joins this Krsna consciousness movement and follows these rules and regulations, material contamination is immediately removed, but one must be careful not to be contaminated again. Therefore these rules and regulations should be followed carefully."
Path of Perfection, Chapter 8
"By executing religious principles under the laws of varna-srama-dharma, one is placed in a comfortable position. One may very easily use his assets for the further advancement of Krsna consciousness. One should understand that the wealth and opportunity one gets in the material world should not be squandered in sense gratification. They are meant for the advancement of Krsna consciousness. This Krsna consciousness movement is therefore teaching people to control the mind and five knowledge-acquiring senses by a definite process. One should practice a little austerity and not spend money on anything other than the regulative life of devotional service. The senses demand that one see beautiful things; therefore money should be spent for decorating the Deity in the temple. Similarly, the tongue has to taste good food, which should be bought and offered to the Deity. The nose can be utilized in smelling the flowers offered to the Deity, and the hearing can be utilized by listening to the vibration of the Hare Krsna mantra. In this way the senses can be regulated and utilized to advance Krsna consciousness. Thus a good position might not be spoiled by material sense gratification in the form of illicit sex, meat-eating, intoxication and gambling. One spoils an opulent position in the material world by driving cars, spending time in nightclubs or tasting abominable food in restaurants. In these ways. the plundering senses take away all the assets that the conditioned soul has acquired with great difficulty."
Srimad-Bhagavatam 5:14:2 Purport
"When a man comes in contact with a saintly person, he becomes aware of the stringent laws of nature and thus becomes a religious person. Irreligious persons are like animals, but in this Krsna consciousness movement such persons can come to a sense of understanding things as they are and abandon the four principles of prohibited activities--namely illicit sex life, meat-eating, gambling and intoxication. This is the beginning of religious life. Those who are so-called religious and indulge in these four principles of prohibited activities are pseudoreligionists. Religious life and sinful activity cannot parallel one another. If one is serious in accepting a religious life, or the path of salvation, he must adhere to the four basic rules and regulations. However sinful a man may be, if he receives knowledge from the proper spiritual master and repents his past activities in his sinful life and stops them, he immediately becomes eligible to return home, back to Godhead. This is made possible just by following the rules and regulations given by the sastra and following the bona fide spiritual master.
At present the whole world is on the verge of retiring from a blind materialistic civilization, which may be likened to hunting animals in the forest. People should take advantage of this Krsna consciousness movement and leave their troublesome life of killing. It is said that the killers of animals should neither live nor die. If they live only to kill animals and enjoy women, life is not very prosperous. And as soon as a killer dies, he enters the cycle of birth and death in the lower species of life. That also is not desirable. The conclusion is that killers should retire from the killing business and take to this Krsna consciousness movement to make life perfect. A confused, frustrated man cannot get relief by committing suicide because suicide will simply lead him to take birth in the lower species of life or to remain a ghost, unable to attain a gross material body. Therefore the perfect course is to retire altogether from sinful activities and take up Krsna consciousness. In this way one can become completely perfect and go back home, back to Godhead."
Srimad-Bhagavatam 4:26:10 Purport
"Actually, those who are in knowledge of everything are determined to execute Krsna consciousness, but those who are rascals (mudhah), sinners (duskrtinah) and the lowest of mankind (naradhamah), who are bereft of all intelligence (mayayapahrta jnanah) and who take shelter of the demoniac way of life (asuram bhavam asritah), are disinterested in Krsna consciousness. As such they become implicated and take on so many activities. Most of these activities center around the killing of animals. Modern civilization is centered around animal-killing. Karmis are advertising that without eating meat, their vitamin value or vitality will be reduced; so to keep oneself fit to work hard, one must eat meat, and to digest meat, one must drink liquor, and to keep the balance of drinking wine and eating meat, one must have sufficient sexual intercourse to keep fit to work very hard like an ass."
Srimad-Bhagavatam 4:27:11 Purport
"Therefore there is no difficulty in coming in contact with the Supreme Lord (ko 'ti-prayasah). On the other hand, going to hell requires great endeavor. If one wants to go to hell by illicit sex, meat-eating, gambling and intoxication, he must acquire so many things. For illicit sex he must arrange for money for brothels, for meat-eating he must arrange for many slaughterhouses, for gambling he must arrange for casinos and hotels, and for intoxication he must open many breweries. Clearly, therefore, if one wants to go to hell he must endeavor very much, but if he wants to return home, back to Godhead, there is no difficult endeavor. To go back to Godhead, one may live alone anywhere, in any condition, and simply sit down, meditate upon the Supersoul and chant and hear about the Lord. Thus there is no difficulty in approaching the Lord. Adanta-gobhir visatam tamisram. Because of inability to control the senses, one must go through great endeavor to go to hell, but if one is sensible he can very easily obtain the favor of the Supreme Personality of Godhead because the Lord is always with him. By the simple method of sravanam kirtanam visnoh, the Lord is satisfied."
Srimad-Bhagavatam 7:7:38 Purport
Bhaktivedanta Book Trust. HDG A.C. Bhaktivedanta Swami Srila Prabhupada.