The brahmacārin led a simple life—he would beg for his food (like a monk) and practice austerities (fasting, chanting, and meditating) to generate spiritual heat (“tapas”) in his body.
By remaining celibate, the student remained pure, and therefore able to receive the wisdom of the holy Veda.
It was believed that retaining semen within one’s body (no ejaculation) would concentrate and therefore increase one’s inner spiritual power. This is why ṛṣīs (hermits) should abstain from sex.