A few years after Srila Prabhupada’s establishing of ISKCON, it became apparent that many of his disciples, despite having practiced devotional service for some time, would again fall away. Such is common in the West, where the fever of sense gratification is so high that certain sinful practices, such as illicit sex and gross intoxication, are considered normal and even desirable; so it is very easy even for practicing devotees to succumb to temptations for indulging in such abominable activities.
It is stated in the Bhagavad-gita (3.36): anicchann api vārșņeya balād iva niyojitah, “being impelled to sinful acts, even unwillingly, as if engaged by force.” Some devotees who actually wanted to be Krsņa conscious were just pulled away as if driven by their senses. To safeguard against such cases, Śrila Prabhupāda wanted to introduce varnāśrama-dharma, the social system given by Krsna (cātur-varnyam mayā srstaṁ guna-karma-vibhägaśaḥ), to help his disciples remain on the standard of Krsna consciousness, by adhering to the four regulative principles and by daily chanting sixteen rounds of the mahā-mantra. Even more ambitiously, Śrila Prabhupäda proposed to regulate all of humankind so that people worldwide may avail of Vedic culture (also termed varņāśrama-dharma, or sanātana-dharma, or the ancient culture of pious Indians), which is more conducive for adopting Krsna consciousness.
Aspiring devotees need to follow varņāśrama-dharma to help them rise to the perfect platform. Māyā is very, very powerful, and to suppose that she is easy to overcome is foolishness, The basic principle of this māyā, of material existence, is the attraction between male and female:
purmsah striyā mithuni-bhāvam etam
tayor mitho hrdaya-granthim ähuh
janasya moho ‘yam aham mameti
The attraction between male and female is the basic principle of material existence. On the basis of this misconception, which ties together the hearts of the male and female, one becomes attracted to his body, home, property, children, relatives and wealth. In this way one increases life’s illusions and thinks in terms of “I and mine”
Varņāśrama-dharma is required to help in overcoming the sexual impulse. As Śrila Prabhupăda explained:
What is the big plan behind these regulative principles? The big plan is: here is the attraction – purmsah striyā mithuni- bhävam – to cut down this attraction between male and female. This is the big plan. Otherwise there is no need of varnäśrama- dharma. Varnăśrama means to train the candidates gradually to become free from this entanglement of man and woman. This is the basic principle.
The entire Vedic system teaches one to avoid sex life so that one may gradually progress from brahmacarya to grhastha, from grhastha to vänaprastha, and from vänaprastha to sannyāsa and thus give up material enjoyment, which is the original cause of bondage to this material world.
However else society may have changed, sexual attraction has not abated. Because sexual attraction is as powerful today as ever before, varnāśrama-dharma is as relevant today as it ever was.
According to the rules of varnāśrama-dharma, men and women are to be separated to a large extent because unless there are systems to regulate the association between men and women, sexual attraction increases, leaving little hope for spiritual advancement. Therefore varnäsrama-dharma society has strict rules to protect both men and women from their lower natures, and especially to preserve women’s respectability and chastity.
 Bg 4.13.  SB 5.5.8.  Lecture, 30 oct 1976  SB 7.12.7, purport