There is no need by any of my disciples to read any books besides my books. In fact, such reading may be detrimental to their advancement in Krsna consciousness–except in certain authorized cases, for example, to read some philosopher like Plato to make an essay comparing his philosophy with Krsna's philosophy. But otherwise, all such outside reading should be stopped immediately. It is simply another botheration. If my students cannot even read my own books thoroughly, why should they read others?

(From a letter from Srila Prabhupada to Sri Govinda)