In plain words
There must be purity in all of them. Only when this purity is brought in does brahmacarya have any meaning.
The student stage is most sacred
A human being is one who is pure, one who is recognised, one who has faith. ‘Mānava’ means one who has faith, they said. Besides this, when we go by the meaning of the words: ‘mā’, ‘nava’. ‘Mā’ means ever. ‘Nava’ means new. This is something ever new! Something that stays new from moment to moment! This very newness is called purity. So, they said, brahmacarya is living out this pure humanness with pure actions and pure feelings. So brahmacarya is not only the actions done with this kind of body, taking the worldly meaning; brahmacarya is understanding the divine principle that lies within, in the mind, and acting by it. For gṛhastha, vānaprastha and sannyāsa, brahmacarya is the most important foundation. That is why the student stage is so sacred. The other three stages too rest on this student stage. This purity enters the other three āśramas too on the strength of whatever results we experience in the student stage. So the foundation of this four-storey building must be very secure. Only when the foundation of the ground floor is very firm will the other three floors be secure too. When the ground floor collapses, the other three floors collapse. So gṛhastha, vānaprastha and sannyāsa rest on brahmacarya.
Brahmacarya is made of purity of body, purity of mind, purity of citta and purity of action
Within brahmacarya we must make our humanness pure.