The main purpose of brahmacharya is the development of the spiritual faculty — the spiritual 'nerve' called medha nadi. When a man practises brahmacharya for ten or twelve years he feels the awakening of this 'nerve' or faculty in him. It is the power of intuition latent in all men. Sri Ramakrishna and Swami Vivekananda have spoken about this. It is not a mere theory.

Moreover, brahmacharya is essential for the nourishment and vigour of the brain. People who do not observe brahmacharya find their brain getting heated up quickly when they try to meditate. Sustained contemplation is impossible unless the brain is strong and cool. Without continence the brain will not be able to withstand the tremendous strain of long hours of meditation.

Reference: Meditation and Spiritual Life by Swami Yatiswarananda (p.209)