Once heard from the spiritual master or teacher, he will remember. He will never forget. Therefore, formerly there was no written book. Sruti, simply by hearing, a brahmacari would be educated, simply by hearing. There was no need of books, writing. Therefore the Vedic literature is known as sruti. It is to be learned by hearing. Even there is book, still, one has to learn it by hearing from the realized soul. Therefore it is called sruti. So this sruti memorizing power should be increased if one observes strictly the life of celibacy. This is the science.