Every person in Sai's Divine mission is an instrument chosen by Swami Himself. Mother Easwaramma was the 'Chosen' mother of Bhagawan Sri Sathya Sai Baba. It can also be said that Prof. N. Kasturi was His chosen biographer. V. K. Narasimhan, who then took-over the reins as the editor of 'Sanathana Sarathi', described him as Swami's Vyasa.
In the initial phase of the Avatar, Sri Kasturi was solely responsible for translating Swami's Discourses, noting down, and then publishing Sai literature, thereby propagating Swami's Life and Teachings to the entire humanity.