The Talmud (Eiruvin 54b) tells the story of Rabbi Prayda, who had a very slow-to-learn student. So much so that Rabbi Prayda would have to review each lesson four hundred times before the boy understood it. One day, when the student was having extra difficulty concentrating, he taught him the same lesson eight hundred times! A heavenly voice then declared, “Rabbi Prayda, in the merit of this act, you and your entire generation will receive the World to Come.” ~ R’ Yaakov Meir Shechter