Man works and toils in order to keep the laws of the nourishments of the body whether knowingly or unknowingly, since the reward and punishment are revealed. For this reason, even if a person does not feel the taste of eating or drinking, such as when he is sick, he still forces himself to eat and drink, even though he does not enjoy these foods, since if he does not observe these laws he will be punished, and not merely punished, but will be punished by death.
This is not so with nourishments of the soul, which are Torah and Mitzvot [commandments]. When one does not find flavor in them, he cannot observe them by force. Rather, to the extent that he believes in reward and punishment, to that extent he observes them. However, the reward and punishment are not revealed to the person, but the nourishments of the soul depend on faith and the measure of faith, and a person cannot always go with faith. Conversely, when the reward and punishment are known, they are strong and clear, and it cannot be said that he has ascents and descents.