“Originally there was only one Veda, and there was no necessity of reading it. People were so intelligent and had such sharp memories that by once hearing from the lips of the spiritual master they would understand. They would immediately grasp the whole purport. But 5,000 years ago Vyasadeva put the Vedas in writing for the people in this age, Kali-yuga. He knew that eventually the people would be short-lived, their memories would be very poor and their intelligence would not be very sharp.” (Shrila Prabhupada, Shri Ishopanishad, Introduction)