A yeshiva student who used to take part in mivtzoyim during his free time (such as on Friday afternoons) wrote to the Rebbe that he did not see any actual results from his work. The Rebbe replied, "He cannot know what goes on in another person's heart. Our Sages said that this is concealed ??? Moreover, our Sages promised that words that come from the heart will enter the heart."

Translated from the Kfar Chabad Magazine