Srila Prabhupada gave us the practical service of distributing his books, and therefore we are able to assist him in spreading Lord Krishna’s glories everywhere. That service is not meant to make us proud or to draw us away from the heart of our practice; it is meant to help us increase our attraction for hearing and chanting. By hearing and chanting, our hearts will become cleansed. “The occupational activities a man performs according to his own position are only so much useless labor if they do not provoke attraction for the message of the Personality of Godhead.” (Bhag. 1.2.8)
Any service that helps us increase such attraction is purifying. Distributing books is particularly purifying because it forces us to speak about Krishna.
(LFD, Vol2, Chanting Purely, Pg 107 and Pg 108)