It is stated that human life is meant for tapasya, austerity. Tapasā. Tapo divyaṁ putrakā yena śuddhyet sattva (SB 5.5.1), that this human form of life is meant for tapasya, not to live like cats and dogs. That is not human form of life. And tapasya, austerity, begins from brahmācārya. Tapasā brahmacaryeṇa śamena damena vā (SB 6.1.13). This is tapasya. Brahmācārya means restraining sex life, celibacy. That is brahmācārya. So when one is serious about advancement of spiritual consciousness, he must live under the control of the guru to learn how to become brahmacārī. This is the main purpose.
The whole Vedic civilization is on the basis of controlling the senses. The yoga practice, it is also meant for controlling the senses. Yoga indriya-saṁyamaḥ. By some artificial bodily exercise one can control the senses. That is called yoga. But one who becomes directly a devotee, his sense control is automatically done, if he is devotee. Bhaktiḥ pareśānubhavo viraktir anyatra syāt (SB 11.2.42). If one is devotee, then he does not like anything material. And the sex enjoyment is the topmost pleasure in this material world. So naturally one who is devotee, he doesn't require to practice brahmācārya separately—paraṁ dṛṣṭvā nivartate (BG 2.59)—because sex pleasure may be very nice in this material world, but when one gets a sense of spiritual pleasure, then this pleasure becomes abominable. It is said by Yamunācārya,
- yad-avadhi mama cetaḥ kṛṣṇa-padāravindayor
- nava-nava-dhāmany rantum āsīt
- tad-avadhi bata nārī-saṅgame
- bhavati mukha-vikāraḥ suṣṭu niṣṭhīvanaṁ ca