Not everybody is capable of renouncing permissible pleasures and making due with little. While such behavior befits the pious, most people are not able to practice such piety and are not expected to do so. It is sufficient for a person to be righteous, refraining only from those things which are forbidden.
However, there are exceptional individuals capable of ascending to extraordinary heights. Such people are able to demand more of themselves.
In general, people differ in character. Some possess greater spiritual capacity and hence more is expected of them. Pious abstinence befits such individuals. They are called upon to distance themselves not only from prohibited matters, but even from overindulgence in permitted pleasures. They are expected to make due with little and to train themselves not to be held sway by their baser inclinations. This, of course, does not imply renouncing necessities without which a person suffers or becomes weak. It is forbidden for a person to deny himself such things. Rather, we are referring to those things which are not necessities, things which it is possible to do without.
abstinence, when practiced by those who are fit for such behavior, refines the inner forces, purifies inclinations and steers them into ideal, spiritual channels. These unique individuals are called upon to be stringent, distancing themselves from all negative elements, even those which are permitted.
We may bring an example of such behavior from R' Yehoshua ben Levi. According to Jewish law, if non-Jews lay siege on a Jewish town and say, "Give us so-and-so. He wronged us and he is hiding is this town, and if you don't hand him over we will conquer the city and kill you all," it is permitted to hand over the accused if he is a wicked person who deserves death. By so doing the entire town will be saved.
R' Yochanan taught that even if the accused is not wicked, if the non-Jews demand a particular individual, it is permitted to hand him over in order to save the town. In fact, there was such a case, and R' Yehoshua ben Levi went to the wanted individual and asked him to hand himself over in order to save the town. The latter heeded R' Yehoshua ben Levi's request and handed himself over.
Now, until this episode, R' Yehoshua ben Levi often experienced revelations of Elijah the Prophet. However, afterwards, Elijah stopped appearing to him. R' Yehoshua ben Levi performed many fasts until finally Elijah reveal himself again:
"I do not reveal myself to those who extradite their brethren" he said.
R' Yehoshua ben Levi replied, "But I only acted according to the law."
"Is this the law adopted by the pious?" said Elijah. True, you acted in accordance with the law, but this is not proper conduct for a pious individual like yourself, and you should not have been involved in handing over the accused.
There are rules of legal conduct and there are rules of pious conduct. A person who is fit for such is called upon to accept the rules of pious conduct. Pious abstinence is not for everybody, but those unique individuals who are able to behave in such a manner have an effect on everybody. Through them the entire population is uplifted.