Before Vyasadeva, all the Vedic Scriptures were taught and received verbally by the disciplic succession. Both the students and the Spiritual Master of those ages were so sharp in their memory that once they heard the transcendental message from the Spiritual Master the message was immediately imprinted in their brain as vivid as a written language. For example, Sukadeva Gosvami was narrating Srimad-Bhagavatam extemporaneously. The whole Srimad-Bhagavatam, eighteen thousand verses, very difficult to pronounce even and what to speak of memorizing, were narrated very easily just like reading some printed book. He narrated the whole subject matter of Srimad-Bhagavatam continuously for seven days and Maharaja Pariksit also understood the subject matter very clearly. Both of them were so meritorious that they attained the highest goal of life, namely the Lotus Feet of Lord Sri Krsna simply by reciting and hearing respectively.
Letter to Bali Mardan, 25 August, 1970