A man once confided in me that when he studies Torah, he is often unsure as to whether or not he understood the material. He must therefore review it over and over again. This causes him untold anguish. Whenever he reviews his learning, he merits revealing new insights into the subject, but this offers him little comfort, for one insight often contradicts another.
When I heard his story, I replied, “How fortunate you are that your suffering comes from Torah study! This is proof that you are plumbing the depths of Torah. It is only natural for Torah study to come through difficulty and exertion. The Torah states (Vayikra 26:3), ‘If you will follow My decrees and observe My commandments,’ upon which Rashi comments (Torat Kohanim, Vayikra, ibid.), ‘That you should labor in the Torah.’
“The Gaon, Rabbi Yisrael Salanter, zt”l, said that one must sweat over the words of Torah in order to be considered laboring in it. It is this toil in Torah which chases away the Yetzer Hara.”