The four divisions of human life, namely the brahmacari, the grhastha, the vanaprastha, and the sannyasi, are all meant to help men become perfect yogis or transcendentalists. Since human life is not meant for our enjoying sense gratification like the animals, the four orders of human life are so arranged that one may become perfect in spiritual life. The brahmacaris, or students under the care of a bona fide spiritual master, control the mind by abstaining from sense gratification. They are referred to in this verse as sacrificing the hearing process and the senses in the fire of the controlled mind. A brahmacari hears only words concerning Krsna consciousness; hearing is the basic principle for understanding, and therefore the pure brahmacari engages fully in harer namanukirtanam—chanting and hearing the glories of the Lord. He restrains himself from the vibrations of material sounds, and his hearing is engaged in the transcendental sound vibration of Hare Krsna, Hare Krsna. Similarly, the householders, who have some license for sense gratification, perform such acts with great restraint. Sex life, intoxication and meat eating are general tendencies of human society, but a regulated householder does not indulge in unrestricted sex life and other sense gratifications. Marriage on principles of religious life is therefore current in all civilized human society because that is the way for restricted sex life. This restricted, unattached sex life is also a kind of yajna because the restricted householder sacrifices his general tendency toward sense gratification for higher transcendental life.